||ICS-13 Abstract View
|Auroral processes and outer electron radiation belt|
|Antonova, E.E., email@example.com (1,2)|
Stepanova, M.V., firstname.lastname@example.org (3)
Kirpichev, I.P., email@example.com (2)
Riazantseva, M.O., firstname.lastname@example.org (2)
Vorobjev, V.G., email@example.com (4)
Yagodkina, O.I., firstname.lastname@example.org (4)
Vovchenko, V.V., email@example.com (2)
Ovchinnikov, I.L., firstname.lastname@example.org (1)
Sotnikov, N.A., email@example.com (1)
Moya, P.S., firstname.lastname@example.org (5)
Pinto, V.A. email@example.com (6)
|Auroral dynamics and acceleration of outer radiation belt electrons for a long time considered as weakly connected processes. At the same time, it was known, that development of magnetospheric substorms is a necessary condition for outer radiation belt filling. It was also well known, that large fluxes of relativistic electrons appear during magnetic storms when the auroral oval move to low latitudes and powerful ring current is developed leading to magnetic field distortions. The radial position of the outer radiation belt maximum formed after magnetic storm is determined by the maximal value of Dst variation during this storm. This position coincides with the maximum of the plasma pressure and with the position the maximal shift of the westward electrojet toward the equator. Such features is difficult to explain on the base of traditional substorm theories and dominant role of magnetotail processes in substorm development. However, the situation becomes clearer after the reanalysis of auroral oval mapping and topology of magnetospheric currents. It was shown that the main part of auroral oval is mapped not to the plasma sheet. It is mapped to the surrounding the Earth plasma ring at geocentric distance from ~6-7Re till 10-13Re where transverse magnetospheric currents are the high latitude continuation of the ordinary ring current. |
We summarize the arguments demonstrating the leading role of auroral processes in the outer radiation belt formation including first auroral arc brightening during storm time substorms, modification of magnetospheric plasma distribution by accelerated ionospheric ions and injections of substrom accelerated electrons in the region of depressed magnetic field. We discuss the possible role of local particle traps in the acceleration of outer belt electrons.
|(1) Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University. Moscow, Russia|
(2) Space Research Institute RAS, Moscow, Russia
(3) Physics Department, Science Faculty, Universidad de Santiago de Chile, Chile
(4) Polar Geophysical Institute, Apatity, Murmansk Region, Russia
(5) Universidad de Chile, Santiago, Chile
(6) Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, USA
|The effect of ion multi-scales on magnetic reconnection in earth's magnetotail -Cluster observations|
|Ardakani, A.S., firstname.lastname@example.org (1)|
Mouikis, C.G., email@example.com(1)
Kistler, L.M., Lynn.firstname.lastname@example.org (1)
Torbert, R., Roy.Torbert@unh.edu (1)
Roytershteyn, V., email@example.com (2)
Omelchenko, Y.A., firstname.lastname@example.org (2)
|A recent statistical study, using Cluster observations, showed that during substorms, a higher O+ content in the plasma sheet during the substorm growth phase, makes it more difficult to trigger reconnection [Liu et al, 2013]. In addition, they showed that, in contrast to predictions that the reconnection rate during the substorm expansion phase slows down in the presence of O+, the unloading rate is actually faster when the O+ content is higher. This could be due to a faster local reconnection rate or due to reconnection occurring over a greater width in the tail when the O+ content of the plasma sheet is high. To address this question, we will use reconnection events observed by Cluster that have different densities of O+ and we will determine the local reconnection rate. We will use the deduced local reconnection rate together with the total magnetotail pressure rate of change to estimate the cross-tail extent of the reconnecting plasma sheet.
|(1) Space Science Center, University of New Hampshire, Durham, NH 03824|
(2) Space Science Institute, Boulder, CO, 80301
|Bursty Bulk Flows: Comparing THEMIS observations with OpenGGCM simulations|
|Arel D., email@example.com (1)|
Raeder, J., J.Raeder@unh.edu (1)
Ferdousi, B., firstname.lastname@example.org (1)
Maynard, K., email@example.com (1)
Cramer, W.D., firstname.lastname@example.org (1)
|THEMIS observations of Bursty Bulk Flow (BBF) events in the Earth's magnetotail feature varying magnetic field (Bz) signatures for the same BBF, such as a dip in Bz which preceeds the flow, as it propagates earthward through the central plasma sheet. It has not been clear whether these variations are due to some aspect of the BBF that is changing in time or due to the geometry of the BBF and the specific location of the spacecraft relative to it. In order to investigate these varying BBF signatures, we use OpenGGCM simulations, which produce realistic looking BBFs. By generating virtual observations at different locations relative to the BBFs, we show that the same BBF produces highly varying signatures depending on the location of the observing satellite. Specifically we show that the dip in Bz seems to depend on whether the satellite is closer to the center of the BBF or on the periphery. This results mainly from the fact that BBFs are not simple one-dimensional structures as they are often depicted in the literature, but rather following more complicated paths in the plasma sheet. In this presentation, we will present a comparison of simulated BBF signatures to those found in the THEMIS observations and use them to infer additional details about the BBF not available to the THEMIS data alone.
|(1) University of New Hampshire, Durham. NH|
|Formation of thin current sheets in the Earth magnetotail|
|Artemyev, A.V., email@example.com (1)|
Angelopoulos, V., firstname.lastname@example.org (1)
Runov, A., email@example.com (1)
Petrukovich, A.A., firstname.lastname@example.org (2)
|Presentation is focused on the current sheet thinning observed in the substorm growth phase. We discuss main properties of the thinning current sheet: evolution of the current density, lobe magnetic field, plasma density, and particle temperatures. Kinetics of thinning current sheets (e.g., contributions of ions and electrons to the current density growing) is discussed. We also provide brief comparison of observed current sheet properties and modern model/simulations describing the thin current sheet formation.
|(1) Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA|
(2) Space Research Institute, RAS, Moscow, Russia
|Multi-Fluid Simulations Including Kinetic Effects of MMS Reconnection Events|
|Bhattacharjee, A., email@example.com (1)|
Hakim, A., firstname.lastname@example.org (2)
Ng, J., email@example.com (1)
TenBarge, J., firstname.lastname@example.org (3)
|Since fully kinetic global electromagnetic simulations of magnetospheric plasmas with realistic plasma parameters and system size remain beyond the capability of present petascale or even planned exascale computers over the next 10 years, there has been significant interest in developing extended multi-fluid equations that incorporate kinetic effects through closure relations. We have developed a multi-fluid moment model in the context of collisionless magnetic reconnection. This model evolves full Maxwell equations along with moments of the Vlasov equation for each species in the plasma. Effects like finite particle inertia and pressure tensor that break field lines are self-consistently included in the model without the need to invoke a generalized Ohm's law. At different levels of truncation---5, 10, and 20 moments---we obtain an increasingly detailed description of reconnection dynamics. Whereas the 5-moment model can be shown to be formally equivalent to Hall MHD (in the limit of vanishing electron inertia and infinite speed of light), it neglects heat flux, which is essential in obtaining results that are in reasonable agreement with the results of fully kinetic simulations. For collisionless plasmas, we have tested the efficacy of nonlocal Hammett-Perkins heat flux closure (which includes Landau damping) at the 10 moment level, and the results of our multi-fluid model are shown to be in very good accord with PIC simulations and validated by MMS observations at the dayside magnetopause. We have further extended the scope of these studies by carrying out multi-fluid, 10-moment simulations of fully three-dimensional kinetic ballooning modes of the Earth's magnetotail (in the presence of other kinetic instabilities) as a viable mechanism for substorm onset.
|(1) Princeton University|
(2) Princeton Plasma Physics Laboratory
(3) University of Maryland, College Park
|Energetic Particles in Substorms|
|Birn, J., email@example.com (1)|
Runov, A., firstname.lastname@example.org (2)
Chandler, M. O., email@example.com (3)
Moore, T. E., firstname.lastname@example.org (3)
|Using a combined MHD and test particle approach, we investigate particle acceleration and energetic particle fluxes associated with substorms, flow bursts, and dipolarization. Specifically we demonstrate properties of ion velocity ditributions, showing good agreement with recent THEMIS and MMS observation. The simulation approach yields acceleration mechanisms and sources responsible for shaping the distributions.
|(1) Space Science Institute, Boulder, CO 80301, USA|
(2) University of California, Los Angeles, California, USA
(3) NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
|Investigating geomagnetic activity controlled by solar wind with different phase front angles using pointwise mutual information|
|Cameron, T.G., email@example.com(1)|
Jackel, B., firstname.lastname@example.org(1)
Oliveira, D.M., email@example.com (2,3)
|Recently, it has been shown that interplanetary shock impact angles play an important role in geomagnetic activity following the shock impact. In general, numerical and experimental results suggest that the more frontal the shock impact, i.e., the more aligned the shock normal vector with the Sun-Earth line, the higher the shock geoefficiency, for instance, the more intense the substorm triggering. In some cases, this result holds even for frontal shocks weaker than inclined shocks. However, the role of solar wind front angles in most common solar wind conditions, or non-shocked solar wind, is yet not well understood. The main goal of this study is to investigate this solar wind feature and its subsequent geomagnetic activity triggering, here represented by an enhanced version of the AE index. Since we use a particularly large amount of data, here represented by the ACE data from 1998 to 2015, we use the pointwise mutual information method to explore shared information between the solar wind phase front angle and the auroral index. Generally, when IMF Bz was directed southward, we found that large geomagnetic activity was connected with solar wind phase fronts with small impact angle, which agrees with the results for shocked solar wind. In the cases when IMF Bz > 0, the peaks of geomagnetic activity occur for solar wind phase front angles close to 45°, or are aligned with the Parker spiral. This configuration corresponds to a favorable scenario for energy input into the magnetosphere, even during nominal or quiet conditions.
|(1) Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada|
(2) NASA Goddard Space Flight Center, Greenbelt, MD USA
(3) Goddard Planetary Heliophysics Institute, University of Maryland, Baltimore County, Baltimore, MD USA
|Characteristic study of double substorm onsets in response to IMF variations|
|Cheng, C.-C., firstname.lastname@example.org (1)|
Russell, C.T., email@example.com (2)
Mann, I.R., firstname.lastname@example.org (3)
Donovan, E., email@example.com (4)
Baumjohann, W., firstname.lastname@example.org (5)
|A study of the characteristics of double substorm onsets in response to variations of the interplanetary magnetic field (IMF) is undertaken with magnetotail and ground observations by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission on 18 March 2009 and 3 April 2009 (Kp ~ 0), and on 16 February 2008 and 24 February 2010 (Kp ~ 2-3). During the time of interest, THEMIS probes at -8 Re > XGSM > -20 Re and 5 Re > YGSM > -5 Re observed earthward flow bursts accompanied by magnetic dipolarizations varying in two stages. The keograms and all sky images close to their footprints showed two consecutive auroral breakups of which the first appeared at lower latitudes than the second. The ground-based magnetometers sensed magnetic bays and perturbations resulting from the formation of substorm current wedge. Two consecutive pulsations in the Pi2-Ps6 band period occurred simultaneously from high to low and very low latitudes. They appeared in the same cycle of growth and then decline in Kyoto-AL. The onset timing of ground pulsations mapped to the solar wind observation just in front of Earth's magnetopause shows their occurrence under an IMF variation cycle of north-to-south and then north. Their dynamic spectrums have the spectral features of double substorm onsets triggered by northward IMF turning. Hence in response to IMF variations, double substorm onsets can be characterized with two-stage magnetic dipolarizations in the magnetotail, two auroral breakups of which the first occurring at lower latitudes than the second, and two consecutive Pi2-Ps6 band pulsations.
|(1) Department of Electronic Engineering, National Formosa University, Hu-Wei 63201, Taiwan|
(2) Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095, USA
(3) Department of Physics, University of Alberta, Edmonton, Alberta T6G 2J1, Canada
(4) Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Canada
(5) Space Research Institute, Austrian Academy of Sciences, Graz 8042, Austria
|Evidence for a magnetotail at criticality|
|Clausen, L. B. N, email@example.com (1)|
Milan, S. E., firstname.lastname@example.org (2)
|We use global maps of field-aligned currents (FACs) provided by the Active Magnetosphere and Planetary Electrodynamic Response Experiment (AMPERE) to automatically find the R1 oval, i.e., the location of the maximum region 1 current in the northern hemisphere. The location of the|
R1 oval is related to the location of the open/closed field line
boundary (OCB) such that integrating the magnetic field within the R1 oval, i.e., across the polar cap, allows us to determine the amount of open magnetic flux f in the magnetosphere as a function of time. We
apply the automated procedure to about 6 years of AMPERE data and obtain just over 1.5 million f measurements. Using f, we determine the size of "unloading events", i.e., events when f decreases for a certain amount of time. We show that the statistics of the unloading events show evidence of finite-size scaling, which indicates that the magnetotail is in a state of criticality. We go on to discuss the implications of this evidence for substorm concept.
|(1) Department of Physics, University of Oslo, Oslo, Norway|
(2) Department of Physics and Astronomy, University of Leicester, Leicester, UK
|Electric Currents in Substorms: Systems versus Distributions|
|Connors, M., email@example.com (1)|
|Idealized systems are ubiquitous in physics: the joke about the spherical cow does not bear repeating. Magnetic measurements give us fundamental information about physical processes during substorms, since magnetic perturbations arise from currents in space. Yet, interpretation of magnetic data, especially from the ground, remains challenging. Is it more useful to regard currents as part of systems or as distributions of current density? The fruitful concept of the Substorm Current Wedge (SCW) derives from ideas of Birkeland over a century ago, expressed as essentially an electric circuit. The competing concept of Chapman envisaged ground magnetic perturbations in substorms as arising from a distribution of current in the ionosphere, much like the global system of the quiet day, and describable by continuous mathematical functions. Fukushima clarified why each interpretation could give the same result on the ground. When explicit detection of the field-aligned currents of the Birkeland view resolved the issue, Fukushima's Theorem lost its context and now seems unhelpful. It presented a field line-ionosphere system with cancelling currents, but enhancements in the vertical magnetic component can arise from Hall currents in a rather similar overall system. The Iijima-Potemra currents have little ground signature due to being essentially solenoidal systems. AMPERE has allowed us a much enhanced view of near-Earth field-aligned currents on a time scale approaching (with caveats) that of substorms. Its density of data is sufficient that gridding into a distribution is appropriate. This leads to considering the overlap with the SCW concept as a system that unifies near-Earth currents and connects them with space. Studies are presented that quantify the SCW from ground magnetic data through simple forward models, with verification of their parameters through comparison to independent AMPERE data. These give a context for placement of observed phenomena relative to the SCW position, applicable both on the ground and in mapping to space. Recent observations are presented stressing the importance of the vertical component, which is highly effective in producing ground induced currents, and can arise through motion of electrojets in substorms, or possibly from the Hall currents in a Fukushima-like system.
|(1) Athabasca University Observatories, Athabasca AB, T9S 3A3 Canada|
|Plasma Sheet Injections into the Inner Magnetosphere: Two-way Coupled OpenGGCM-RCM model results|
|Cramer, W.D., firstname.lastname@example.org (1)|
Raeder, J., email@example.com (1)
Toffoletto, F.R., firstname.lastname@example.org (2)
Gilson, M., email@example.com (1,3)
Hu, B., firstname.lastname@example.org (2,4)
|Plasma sheet injections associated with low flux tube entropy bubbles have been found to be the primary means of mass transport from the plasma sheet to the inner magnetosphere. A two-way coupled global magnetosphere-ring current model, where the magnetosphere is modeled by the OpenGGCM MHD model and the ring current is modeled by the Rice Convection Model (RCM), is used to determine the frequency of association of bubbles with injections and inward plasma transport, as well as typical injection characteristics. Multiple geomagnetic storms and quiet periods are simulated to track and characterize inward flow behavior. Dependence on geomagnetic activity levels or drivers is also examined.
|(1) Space Science Center, University of New Hampshire, Durham, New Hampshire, USA|
(2) Department of Physics and Astronomy, Rice University, Houston, Texas, USA
(3) Pattern Technologies Inc., Mountain View, California, USA
(4) CGG Services, Houston, Texas, USA
|Estimating equatorial daytime vertical E×B drift velocities from magnetic field variations|
|Diaby, K.A.A., email@example.com (1)|
Obrou, O.K., firstname.lastname@example.org (1)
|Accurate measurement and prediction of the vertical plasma drift is important for the study of many physical processes in the low-latitude ionosphere. Equatorial E×B drift velocities are significant input parameters that go into many ionospheric models, because they help describe vertical plasma motions near the magnetic equator. A previous work done by Anderson et al.(2004) has demonstrated the ability to derive Peruvian longitude sector, daytime vertical E×Bdrifts from ground-based magnetometer data and have derived the ∆H versus E×B relationships. The present research extends the same method to the West African longitude sector. We use magnetic field data of Conakry, Guinea (-0.46°, 60.37°) and Abidjan, Cote d'Ivoire (-6°, 65.82°) from the African Meridian B-field Education and Research (AMBER) network. On the basis of data availability, 9 magnetically quiet days have been analyzed and showed that the Peruvian DH versus E×B relationships is applicable to the West African longitude sector.
|(1) Laboratoire de Physique de l'Atmosphère et Mécanique des Fluides, Université Felix Houphouët Boigny, 22 B.P. 582, Abidjan 22, Côte d'Ivoire|
|MAVEN observations of substorm-like processes in the Martian magnetosphere|
|DiBraccio, GA, email@example.com (1)|
|The Martian magnetosphere is a dynamic environment, formed as the interplanetary magnetic field (IMF) interacts with the planet's ionosphere and upper atmosphere. This scenario, however, is complicated by the existence of Mars' crustal magnetic fields, which are able to deflect the solar wind and reconnect with the IMF. Therefore, the combination of the draped IMF and localized planetary fields creates a hybrid magnetosphere with characteristics that are similar to both induced (e.g., Venus) and intrinsic (e.g., Earth) magnetospheres. For comparison to intrinsic magnetospheres, observations have revealed that substorm-like signatures are present at Mars. Here, we report on results from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, which has been providing continuous plasma and magnetic field measurements of the Mars space environment since orbit insertion in September 2014. From these data, MAVEN has observed both local and global phenomena that are often associated with substorms at Earth. In the magnetotail, magnetic reconnection is observed to statistically occur in the near-Mars current sheet at ~1.3 RM (where RM is the radius of Mars) downtail from the planet. MAVEN observations have revealed Hall field signatures associated with these reconnection events, while Alfvénic outflow jet observations are limited due to local Alfvén speeds on the order of ~10 km/s. Also within the tail current sheet, magnetic flux ropes are observed both individually and as a chain of events, indicating the magnetic reconnection is responsible for the transport of flux both tail- and planet-ward. On a global scale, MAVEN observations have revealed a period of repetitive loading and unloading of tail magnetic flux. During this interval the field magnitude dramatically increases and decreases, exhibiting signatures similar to substorm activity within intrinsic magnetospheres. While Mars' magnetosphere is a unique environment in our solar system, we can use comparisons to both induced and intrinsic magnetospheres to develop an understanding of the dynamics driving the system.
|(1) NASA Goddard Space Flight Center, Greenbelt, MD 22042|
|Evidence of kinetic Alfvén eigenmode in the near-Earth magnetotail during substorm expansion phase|
|Duan S.P., firstname.lastname@example.org (1)|
Dai L., email@example.com (1)
Wang C., firstname.lastname@example.org (1)
Liang J., email@example.com (2)
Lui A. T. Y., firstname.lastname@example.org (3)
Chen L.J., email@example.com (4)
He Z.H., firstname.lastname@example.org (1)
Zhang Y. C., email@example.com (1)
Angelopoulos V., firstname.lastname@example.org (5)
Cai C.L., email@example.com (1)
Reme H., Henri.Reme@irap.omp.eu(6)
Dandouras I., Iannis.Dandouras@irap.omp.eu(6)
|Unipolar pulses of Kinetic Alfvén wave (KAW) are first observed in the near-Earth plasma sheet (NEPS) associated with dipolarizations during substorm expansion phases. Two similar events are studied with THEMIS observations during substorms on 3 February 2008 and 7 February 2008. The unipolar pulses were located at a trough-like Alfvén speed profile in the northern plasma sheet at a distance of 10-11 RE from Earth. The dominant wave components consist of a southward δEz toward the neutral plane and a +δBy toward the dusk. The |δEz|/|δBy| ratio was in the range of a few times of the local Alfvén speed, a strong indication of KAW nature. The wave Poynting flux was earthward and nearly parallel to the background magnetic field. The pulse was associated with an earthward field-aligned current carried by electrons. These observational facts strongly indicate a KAW eigenmode that is confined by the plasma sheet but propagates earthward along the field line. The KAW eigenmode were accompanied with short timescale (1min) dipolarizations likely generated by transient magnetotail reconnection. The observed polarity of the KAW field/current is consistent with that of the Hall field/current in magnetic reconnection, supporting the scenario that the Hall fields/current propagate out from reconnection site as KAW eigenmodes. Aurora images on the footprint of THEMIS spacecraft suggest that KAW eigenmode (KAWE) may power aurora brightening during substorm expansion phase. During intense substorms, The KAWE with the large perpendicular unipolar electric field, Ez ~ -20 mV/m, significantly accelerate O+ ions in the direction perpendicular to the background magnetic field observed by Cluster in the NEPS. The change of the move direction of O+ ions is useful for O+ transferring from the lobe into the central plasma sheet in the magnetotail. Thus KAWE can play an important role in O+ ions transfer process from the lobe into the plasma sheet during intense substorms.
|(1) State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, China|
(2)Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada
(3) Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland 20723, USA
(4) Department of Physics, University of Texas at Dallas, Richardson, Texas, USA
(5) Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA
(6) University of Toulouse, UPS-OMP, IRAP, Toulouse, France
|Pitch angle scattering of energetic electrons by bursty bulk flows (BBFs)|
Hudson, M., firstname.lastname@example.org(1)
|The pitch angle scattering of energetic electrons (≥ 10s keV) caused by the spatial variation of the fields associated with bursty bulk flows (BBFs) has been simulated using the output fields of the Lyon-Feddor-Mobarry (LFM) global magneto-hydrodynamic (MHD) code . The MHD code was run with specified solar wind conditions so as to reproduce the observed qualitative picture of the BBFs .|
The electrons trajectories were traced by integrating the Lorentz equation using a simplectic volume preserving algorithm . The result of the simulation shows that the violation of conservation of the first adiabatic invariant occurs as the electrons cross a weak mag- netic field region with a strong gradient. This resulted in the pitch angle scattering of the particles. The mechanism is similar to the choatic scattering of the pitch angle in the current sheet previously described . The scattering in pitch angle due to the BBFs can occur throughout the outer magnetosphere where there are BBFs, unlike the scattering by the current sheet which is limited to the central plasma sheet region.
 He, Y., Sun, Y., Liu, J., and Qin, H. (2015), Volume-preserving algo- rithms for charged particle dynamics, Journal of Computational Physics 281, 135147, doi.org/10.1016/j.jcp.2014.10.032
 Lyon,J. G., Fedder, J. A., and Mobarry, C.M., The Lyon- Fedder-Mobarry (LFM) Global MHD Magnetospheric Simulation Code (2004), J. Atm. And Solar-Terrestrial Phys., 66, Issue 15-16, 1333- 1350,doi:10.1016/j.jastp.
 Wiltberger, Merkin, M., Lyon, J. G., and Ohtani, S. (2015), High-resolution global magnetohydrodynamic simulation of bursty bulk flows, J. Geophys. Res. Space Physics, 120, 45554566, doi:10.1002/2015JA021080.
 Burkhart, G. R., and Chen, J.(1992), Chaotic Scattering of Pitch Angles in the Current Sheet of the Magnetotail, J. Geophys. Res., 97, 6479-6491
|(1)Department of Physics and Astronomy, Dartmouth College, Hanover, NH,03755|
(2) NCAR-HAO, Boulder, CO, 80303
|Auroral streamers as Ionospheric Footprints of the Bursty Bulk Flows|
|Ferdousi, Banafsheh, email@example.com (1)|
Raeder, Joachim, J.Raeder@unh.edu (2)
Cramer, Doug, firstname.lastname@example.org (2)
Zesta, Eftyhia, email@example.com (3)
Murphy, Kyle, firstname.lastname@example.org (3)
|In-situ measurements in the magnetotail are sparse and limited to single points. In the ionosphere, on the other hand, there is a broad range of observations, including magnetometers, aurora imagers, and radars . Since the ionosphere is the mirror of the plasmasheet, it can be used as a monitor of the magnetotail dynamics. Thus, it is of great importance to understand the coupling process between the ionosphere and the magnetosphere in order to interpret the ionosphere and ground observations properly. For this purpose, the global magnetohydrodynamic simulation model, OpenGGCM model, is used to investigate such a coupling processes. Bursty bulk flows (BBFs) which are identifiable as aurora streamers in the ionosphere are important processes that greatly contribute to convection of the tail. This study focuses on mapping such flows from the magnetotail to the ionosphere along the magnetic filed lines for three states of the magnetotail: before the substorm onset, during substorm expansion, and during steady magnetic convection event.
|(1) University of California, Los Angeles, CA 90095|
(2) University of New Hampshire, Durham, NH 03824
(3) Nasa Goddard Center, Greenbelt, MD 20771
|What effect do substorms have on the radiation belts?|
|Forsyth, C (1) |
Watt, CEJ (2)
Rae. IJ (1)
Murphy, KR (3)
Freeman, MP (4)
Huang, C.-L (5)
Spence, HE (5)
Boyd, AJ (6)
Coxon, JC (7)
Jackman, CM (7)
Kalmoni, NME (1)
|It is commonly thought that substorms are a key driver of enhancements of energetic electrons in the inner magnetosphere that make up the radiation belts. The injection of mid-energy (~100 keV) electrons by substorm activity leads to the generation of electromagnetic waves that resonantly interact with an existing low-energy (sub keV) electron population, energising them up to high (MeV) energies. However, the extent to which substorms impact on the radiation belts over a range of timescales is yet to be fully understood. In this study, we examine the occurrence of increases and decreases in the total radiation belt electron content (TRBEC) of 1000 MeV/G electrons calculated from the Van Allen Probes with respect to geomagnetic activity from the SuperMAG AL (SML) index and substorm periods determined by SOPHIE [Forsyth et al, 2015]. Our results show that the radiation belts are inherently lossy, with up to a 70% probability that TRBEC will be decreasing following a quiet interval. Following substorm activity, this probability reduces to 50%. When TRBEC is increasing, the rate of increase is correlated with SML and SYMH. In contrast, the rate of decrease is independent of activity levels. Thus, while substorm activity has a significant impact on changes in the radiation belts, it is somewhat simplistic to expect substorm activity to their total electron content.
|(1) UCL Mullard Space Science Laboratory, UK|
(2) University of Reading, UK
(3) NASA Goddard Space Flight Center, USA
(4) British Antarctic Survey, UK
(5) University of New Hampshire, USA
(6) New Mexico Consortium
(7) University of Southampton, UK
|Characterizing the Meso-scale Flows in Earth's Coupled Magnetosphere-Ionosphere-Thermosphere System|
|Gabrielse, C., email@example.com (1)|
Nishimura, Y., firstname.lastname@example.org (1), (2)
Lyons, L., email@example.com (1)
Gallardo-Lacourt, B., firstname.lastname@example.org, (3)
Deng, Y., email@example.com (4)
|NASA's Heliophysics Decadal Survey put forth several imperative, Key Science Goals. The second goal communicates the urgent need to "Determine the dynamics and coupling of Earth's magnetosphere, ionosphere, and atmosphere and their response to solar and terrestrial inputs...over a range of spatial and temporal scales." Sun-Earth connections (called Space Weather) have strong societal impacts because extreme events can disturb radio communications and satellite operations. The field's current modeling capabilities of such Space Weather phenomena include large-scale, global responses of the Earth's upper atmosphere to various inputs from the Sun, but the meso-scale (~50-500 km) structures that are much more dynamic and powerful in the coupled system remain uncharacterized. Their influences are thus far poorly understood. We aim to quantify such structures, particularly auroral flows and streamers, in order to create an empirical model based on activity level (AL index), season, solar cycle (F10.7), interplanetary magnetic field (IMF) inputs, etc. We present a statistical study of meso-scale flow channels in the nightside auroral oval and polar cap using SuperDARN. These results are used to inform global models such as the Global Ionosphere Thermosphere Model (GITM) in order to evaluate the role of meso-scale disturbances on the fully coupled magnetosphere-ionosphere-thermosphere system. Measuring the ionospheric footpoint of magnetospheric fast flows, our analysis technique from the ground also provides a 2D picture of flows and their characteristics during different substorm activity levels that spacecraft alone cannot.
|(1) University of California, Los Angeles; Los Angeles, CA 90025|
(2) Boston University; Boston, MA 02215
(3) University of Calgary; Calgary, AB, Canada
(4) University of Texas, Arlington; Arlington, TX 76019
|Do substorms play a role in energizing the inner magnetosphere?|
|Gabrielse, C., firstname.lastname@example.org (1)|
Gkioulidou, M., Malamati.Gkioulidou@jhuapl.edu (2)
|Historically, the term substorm was coined by Professor S. Chapman in the 1960's to refer to the notion that they are smaller-scale events that build up a geomagnetic storm, and hence the ring current. Many observations and simulations have shown that injections play a significant role in cumulatively feeding the ring current [e.g. Akasofu et al., 1974; Gkioulidou et al., 2014; Yang et al., 2015]. However, several observations demonstrate a disconnect in our understanding of the relationship of smaller-scale magnetospheric injections that deliver energy to the ring current and the definition of the auroral substorm [Ohtani et al., 2006; Dubyagin et al., 2011; Sergeev et al., 2012]. Intriguing observations of similar types of injections have also been made in other planetary magnetospheres such as those of Jupiter and Saturn [Kasahara et al., 2010; Jackman et al., 2013] that may illuminate the general nature of this problem.|
Substorm particle injections are also known to provide a seed population to the radiation belts that can be further energized via wave-particle interactions and transport. Because the injected populations are anisotropic, they can generate the whistler-mode chorus waves capable of both accelerating them to MeV energies as well as scattering them into the loss cone. The balance of sources and losses in the radiation belts is a complex problem, such that the radiation belts respond differently to similar storms [Reeves et al., 2003]. This is further illustrated by recent statistics [Forsyth et al., 2016] showing that only 50% of substorms result in enhanced total radiation belt electron content. What role substorms play in energizing the inner magnetosphere is an open question, one which we intend to discuss with the community in this Socratic Dialogue.
|(1) University of California, Los Angeles, CA 90025|
(2) John Hopkins University Applied Physics Lab, Laurel, MD 20723
|Extensive electron transport and energization via multiple, localized dipolarizing flux bundles|
|Gabrielse, C., email@example.com (1)|
Angelopoulos, V., firstname.lastname@example.org (1)
Artemyev, A., email@example.com (1)
Harris, C., firstname.lastname@example.org (1)
Runov, A., email@example.com (1)
|Using an analytical model of multiple dipolarizing flux bundles (DFBs) embedded in earthward traveling bursty bulk flows, we demonstrate how equatorially mirroring electrons can travel long distances and gain hundreds of keV from betatron acceleration. The model parameters are constrained by four Time History of Events and Macroscale Interactions during Substorms satellite observations, putting limits on the DFBs' speed, location, and magnetic and electric field magnitudes. We find that the sharp, localized peaks in magnetic field have such strong spatial gradients that energetic electrons ∇B drift in closed paths around the peaks as those peaks travel earthward. This is understood in terms of the third adiabatic invariant, which remains constant when the field changes on timescales longer than the electron's drift timescale: An energetic electron encircles a sharp peak in magnetic field in a closed path subtending an area of approximately constant flux. As the flux bundle magnetic field increases the electron's drift path area shrinks and the electron is prevented from escaping to the ambient plasma sheet, while it continues to gain energy via betatron acceleration. When the flux bundles arrive at and merge with the inner magnetosphere, where the background field is strong, the electrons suddenly gain access to previously closed drift paths around the Earth. DFBs are therefore instrumental in transporting and energizing energetic electrons over long distances along the magnetotail, bringing them to the inner magnetosphere and energizing them by hundreds of keV.
|(1) University of California, Los Angeles; Los Angeles, CA 90025|
|Injection Propagation: A View from Space and the Ground|
|Gabrielse, C., firstname.lastname@example.org (1)|
Spanswick, E., email@example.com (2)
Nishimura, Y., firstname.lastname@example.org (1), (3)
Angelopoulos, V., email@example.com (1)
Lyons, L., firstname.lastname@example.org, (1)
Donovan, E., email@example.com, (2)
|The injection region's propagation has been heavily studied at geosynchronous orbit, where substorms were initially studied in-depth. With the launch of new missions providing more data points throughout the tail, observations of particle energization could be extended beyond geosynchronous orbit. We explore the injection region's propagation using the injection database from THEMIS [Gabrielse et al., 2014], which collected data from GEO out to ~20 RE. We compare multi-point observations in space with all-sky-imagers and riometers on the ground, the latter of which provide a 2D picture to supplement the satellite measurements. Although the separated satellites observe dipolarization, fast flows, electric fields, and particle injection almost simultaneously-which could indicate a wide injection region-ground observations make it clear that azimuthal (westward) and poleward (tailward) propagation occurs after initiating in a localized region. The picture supports a paradigm in which a very localized injection region forms in space and expands azimuthally and radially along with the substorm current wedge, magnetic flux pile-up, and azimuthal and poleward expansion of the aurora and particle precipitation (as seen by the riometer chain). The azimuthal expansion occurs quickly in space, which is seen by the spacecraft as they are engulfed by the dipolarization and injection region almost simultaneously. The earthward flows consistently seen at the beginning of dipolarization and injection indicate their continued presence and contribution throughout the expansion.
|(1) University of California, Los Angeles; Los Angeles, CA 90025|
(2) University of Calgary; Calgary, AB, Canada
(3) Boston University; Boston, MA 02215
|Energetic Particle Injections into the Inner Magnetosphere: Relation to Tail Dynamics, Morphology, and Effects on the Near-Earth Space Environment|
|Gkioulidou, M., firstname.lastname@example.org (1)|
Ukhorskiy, A. Y., email@example.com (1)
Mitchell, D. G., Donald.G.Mitchell@jhuapl.edu (1)
Ohtani, S., Shin.Ohtani@jhuapl.edu (1)
Lanzerotti, L. J., firstname.lastname@example.org (2)
|Plasma transport and energization of ions in the magnetotail has been shown to largely occur in the form of injections of hot plasma, localized in MLT, associated with bursty bulk flows and sharp dipolarizations of the magnetic field. However, the relationship of these transient tail phenomena to energetic particle injections|
into the inner magnetosphere is not well understood. The Van Allen Probes, in elliptical orbit with apogee at 5.8 Re, are continuously sampling the near-Earth magnetosphere, inside geosynchronous orbit. The Van Allen Probes' orbital configuration, in combination with the high energy and temporal resolution particle instrumentation as well as magnetic and electric field instrumentation on board, has enabled not only the observation of numerous energetic particle injections deep into the inner magnetosphere, but also their comprehensive investigation of their morphology and the physical processes associated with them. Furthermore, coordination of those observations with ground-based magnetometers for a more global perspective, as well as in situ measurements in the plasma sheet, has shed light on the relation of the energetic particle injections inside geosynchronous with tail dynamics. We present analysis of energetic particle injection events occurring during i) an isolated substorm, and ii) a geomagnetic storm. During the isolated substorm, our results indicate that there are different spatial (narrow vs. wide) and temporal scales (short vs. long) at which injections can occur in the inner magnetosphere. During the geomagnetic storm, frequent meso-scale proton injections were observed deep into the inner nightside magnetosphere, providing a robust mechanism for transporting energetic ions inside geosynchronous orbit. Based on the properties of those injections, we estimate their contribution on the pressure buildup during the storm, and we find it to be substantial.
|(1) Johns Hopkins University/Applied Physics Laboratory, 11101 Johns Hopkins Rd, Laurel, MD 20723 |
(2) New Jersey Institute of Technology, Edison NJ
|On the origin of plasma sheet reconfiguration during the substorm growth phase|
|Gordeev, E., email@example.com (1)|
Sergeev, V., firstname.lastname@example.org (1)
Merkin, V., Slava.Merkin@jhuapl.edu (2)
Kuznetsova, M., email@example.com (3)
|Recently Hsieh and Otto  suggested that transport of the closed magnetic flux to the dayside reconnection region may be the key process which controls the reconfiguration of magnetotail during the substorm growth phase (GP). To test their suggestion we investigated the origin of the near-Earth plasma sheet evolution during the GP using the Lyon-Fedder-Mobarry global MHD model, which (among community-available models hosted at CCMC) is most closely resemble the generic substorm-like behavior [Gordeev et al., 2017]. We confirm that magnetotail reconfiguration is essentially a 3D process which cannot be fully described based on 2D-like tail evolution powered by magnetic flux loading into the lobes. We found that near-Earth return convection strength on the nightside is directly related to the intensity of dayside reconnection, which causes the formation of anti-sunward azimuthal pressure gradients that force plasma to flow towards the dayside magnetopause. This near-Earth part of global convection develops immediately after the onset of dayside reconnection and reaches a quasi-steady level in 10 - 15 minutes. Its magnitude exceeds the total sunward flux transport in the midtail plasma sheet at X≈ -20 RE by an order of magnitude, causing significant amount (0.1 - 0.2 GWb) of closed magnetic flux to be removed from the near Earth plasma sheet during moderate GP. In that region the Bz depletion and current sheet thinning are closely related to each other, and the local Jy(Bz) relationship in the simulations matches reasonably well the power law expression found in the plasma sheet in the same distance [Artemyev et al., 2016], indicating the similar way of system evolution. In summary, global simulations confirm quantitatively that near-Earth return convection is primarily responsible for the severe depletion of the closed magnetic flux in the plasma sheet, major tail stretching and current sheet thinning in the near magnetotail at r<15 RE during the GP of substorm.
|(1) Department of Earth's Physics, Saint Petersburg State University, Saint-Petersburg, Russia|
(2) Applied Physics Laboratory, John Hopkins University, Laurel, MD, USA
(3) NASA Goddard Space Flight Center, Greenbelt, MD, USA
|Looking South for the Northern Light: Substorm Physics as University Curriculum|
|Haaland, Stein, Stein.Haaland@uib.no (1,2)|
Baddeley, Lisa (3),
Olafsson, Kjartan (1),
Ostgaard, Nikolai (1),
Partamies, Noora (3),
Tanskanen, Eija (4),
Vaivads, Andris (5)
|The auroral breakup is one of the most fascinating and intriguing manifestations of magnetospheric substorms. Being exposed to the northern lights, auroral physics and the associated magnetospheric |
processes have been important elements in the space physics curriculum in many Universities in the Nordic countries. For more than 10 years, a cooperation of Norwegian Universities, has offered a special graduate course on substorm physics. This course is presently held at the University Studies in Svalbard, located at 78 deg latitude. The infrastructure on Svalbard provides researchers and students with a unique opportunity to observe substorms and their auroral signatures from a location poleward of the nightside auroral oval. Key elements of the substorm evolution, such as convection changes, motion of the open-closed field line boundary and changes in ionospheric conductance can be studied with on-site radars. A wide range of optical instruments can provide characterization of the aurora. In this talk, we present some of the observational highlights obtained during the field work part of
this special course.
|(1) Birkeland Centre for Space Science, Bergen, Norway|
(2) Max-Planck Institute for Solar System Research, Goettingen, Germany
(3) The University Centre in Svalbard, Svalbard, Norway
(4) Aalto University, Aalto, Finland
(5) Swedish Institute of Space Physics, Uppsala, Sweden
|Heikkila, Walter J., firstname.lastname@example.org (1)|
|By Kirchhoff's Current Law, the algebraic sum of the currents entering and leaving a node must be equal to zero. If there is only one current, the dissipation current denoted by E.J > 0, that cannot be done. A closed circuit path must exist. We need another current, a dynamo current with E.J < 0, to denote the source of energy. Standard Magnetic Reconnection (SMR) is thereby falsified. Schindler et al.  have systems where the current is closed, denoted by General Magnetic Reconnection (GMR). GMR must be used to discuss magnetic connectivity. According to Pontin , if one follows magnetic field lines from foot points comoving in the ideal flow they appear to split as soon as they enter the non-ideal region and their connectivity changes continually and continuously as they pass through the non-ideal region. Experiments show that the low latitude boundary layer on closed magnetic field lines are explained by GMR both at the magnetopause and magnetotail.
|(1) University of Texas at Dallas, 800 west Campbell road, Richardson, TX|
|Plasma dynamics in the Earth's space environment|
|Heikkila, Walter, email@example.com (1)|
|Plasma dynamics in the Earth's magnetosphere is driven by the solar wind and interplanetary magnetic field (IMF) impinging the Sunward boundary of the internal geomagnetic field. Events studies confirm that the injected ions flow essentially tailward with a velocity comparable to the magnetosheath flow, and that the energy spectra inferred for the source population resemble magnetosheath spectra. Phan and Paschmann (1994) have studied 38 low-latitude, dayside (0800-1600 LT) magnetopause crossings by the AMPTE/IRM satellite to investigate this effect. The structures of the key plasma parameters and the magnetic field and the dynamics of plasma flows in this region depend strongly on the magnetic shear across the magnetopause, that is, on the angle between the magnetosheath magnetic field and the geomagnetic field. When the magnetic shear is low (<30°) a magnetosheath transition layer, also called the "plasma depletion layer", of 10-min average width exists where the magnetosheath magnetic field piles up against the magnetopause. When the magnetic shear across the magnetopause is high (>60°), the near-magnetopause magnetosheath is more disturbed with substorm activity.|
Where does this plasma go? The only plausible answer is the low latitude boundary layer just inside the magnetopause, on closed field lines. Figure 7.35 shows two cases: the magnetic shear is high (>60°) in the first case, in the second case magnetic shear is low (<30°). With low shear (where it cannot enter), the entry point is further downstream and returns to the frontside in the boundary layer in the sunward sense producing Theta aurora. The incoming plasma is not spatially restricted to a thin layer attached to the magnetopause (LLBL) but constitutes an entity occupying a substantial part of the magnetotail. The flow in the boundary layer; in either case, is massive enough that it must keep on going because of momentum considerations.
|(1) University Texas Dallas|
|The Role of Auroral Streamers, Pseudo-Breakups, and Substorms in Particle Energization|
|Henderson, M.G., firstname.lastname@example.org (1)|
Morley, S.K., email@example.com (1)
Woodroffe, J.R., firstname.lastname@example.org (1)
Jordanova, V.K., email@example.com (1)
|Dispersionless and dispersed particle injections associated with substorms have been studied for many years based on observations acquired primarily at geosynchronous orbit. A general picture that has emerged is that particles are energized and rapidly transported/organized behind an "injection boundary" that penetrates closer to Earth in some magnetic local time sector (e.g. the so-called double-spiral injection boundary model). Although this seems to provide a very good description of injections at geosynchronous orbit, recent observational and modeling studies have shown that the picture is often more complex farther downtail. It is currently thought that particle injections result when electrons and ions become energized as they interact with the more localized strong dynamic electric and magnetic fields associated with Earthward-directed flow bursts produced at reconnection sites. The details of how this mechanism leads to the formation of a more coherent, broad "injection boundary" structure in the inner magnetosphere is not currently understood.|
We examine this problem using multi-point observations of energetic particle injections together with global auroral imagery. Since auroral streamers and torches are produced by flow bursts (and their near-Earth braking) in the tail, they can be used to understand how observed particle injections relate (spatially and temporally) to the flow bursts. During disturbed intervals, we find that strong injections at geosynchronous orbit are typically associated with new pseudo-breakups and substorm onsets rather than with large-scale streamers and torch structures (although there are in fact cases where the later can lead to strong injection activity.) Simulated injections using the SHIELDS Particle Tracing Model (PTM) are presented as an organizing framework.
|(1) Space Science and Applications, Los Alamos National Laboratory, Los Alamos NM, USA|
|Double Magnetic Reconnection Driven by Kelvin-Helmholtz Vortices|
|Horton, W., firstname.lastname@example.org, (1)|
M. Faganello,email@example.com , (2)
F. Califano, (3)
F. Pegoraro (3)
D. Borgogno (3)
|Simulations and theory for the solar wind driven magnetic reconnection in the flanks of the magnetopause is shown to be intrinsically 3D with the secular growth of couple pairs of reconnection regions off the equatorial plane. We call the process double mid-latitude reconnection and show supporting 3D simulations and theory descripting the secular growth of the magnetic reconnection with the resulting mixing of the solar wind plasma with the magnetosphere plasma. The initial phase develops Kelvin-Helmholtz vortices at low-latitude and, through the propagation of Alfvén waves far from the region where the stresses are generated, creates a standard quasi-2D low latitude boundary layer magnetic reconnection but off the equatorial plane and with a weak guide field component. The reconnection exponential growth is followed by a secularly growing nonlinear phase that gradually closes the solar wind field lines on the Earth.|
The nonlinear field line structure provides a channel for penetration of the SW plasma into the MS as observed by spacecraft [THEMIS and Cluster]. The simulations show the amount of solar wind plasma brought into the magnetosphere by tracing the time evolution of the areas corresponding to double reconnected field lines with Poincaré-like maps. The results for the solar wind plasma brought into the magnetosphere seems consistent with the observed plasma transport. Finally, we have shown how the intrinsic 3D nature of the doubly reconnected magnetic field lines leads to the generation of twisted magnetic spatial structures that differ from the quasi-2D magnetic islands structures.
1M. Faganello, F. Califano, F. Pegoraro, and T. Andreussi, Europhys. Lett. 100, 69001 (2012)
2D. Borgogno, F. Califano, M. Faganello, and F. Pegoraro, Phys. Plasmas 22, 032301 (2015)
3A. Otto and D. H. Fairfield, J. Geophys. Res. 105, 21175, doi:10.1029/ 1999JA000312 (2000).
|(1) University of Texas at Austin, Austin, TX USA|
(2) Aix-Marseille University, CNRS, PIIM UMR 7345, 13397 Marseille, France
(3) Physics Department, University of Pisa, 56127 Pisa, Italy
|Thermospheric response to substorms as observed by the SABER instrument|
|Hunt, L.A., Linda.A.Hunt@nasa.gov (1)|
Mlynczak, M.G., firstname.lastname@example.org (2)
Tsurutani, B.T., email@example.com (3)
Gjerloev, J.W., Jesper.Gjerloev@jhuapl.edu (4)
Russell, J.M., James.Russell@HamptonU.edu (5)
|Infrared radiation, from nitric oxide (NO) at 5.3 μm and carbon dioxide (CO2) at 15 μm, is the dominant mechanism by which the thermosphere cools to space. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite has been measuring thermospheric cooling by NO and CO2 since January, 2002. Physically, changes in NO emission are due to changes in temperature, atomic oxygen, and the NO density, while for CO2, the emission change is most directly related to temperature and atomic oxygen. These physical changes are driven by changes in solar irradiance and geomagnetic conditions. In recent analyses of solar storm impacts, we find infrared cooling effects at the sub-storm level on the order of minutes. These findings provide valuable insight into the global infrared energy budget and chemistry of the thermosphere over a variety of time periods.
|(1) Science Systems and Applications, Inc., Hampton, VA 23666 USA |
(2) NASA Langley Research Center, Hampton, VA 23681 USA
(3) NASA Jet Propulsion Lab, Pasadena, CA, 91109 USA
(4) Johns Hopkins University Applied Physics Lab, Laurel, MD, 20723 USA
(5) Center for Atmospheric Sciences, Hampton University, Hampton, VA, 23668 USA
|Simultaneous observation of auroral substorm onset in Polar satellite global images and ground-based all-sky images|
|Ieda, A., firstname.lastname@example.org (1)|
|Substorm onset has originally been defined as a longitudinally extended sudden auroral brightening ("Akasofu initial brightening"), which is followed a few minutes later by an auroral poleward expansion in ground-based all-sky images.|
In satellite-based global images, in contrast, such a clearly marked two-stage development has not been evident, and instead, substorm onsets have been identified as localized sudden brightenings, which immediately expand poleward.
To resolve these differences, optical substorm onset signatures in global images and all-sky images were compared for a substorm that occurred on 7 December 1999.
We have used the Polar satellite ultraviolet global images with a fixed filter (170 nm), enabling a high time resolution (37 s), and have used the 20 s resolution green line (557.7 nm) all-sky images at Muonio in Finland for comparison.
Accordingly, the substorm onset in the all-sky images consisted of the Akasofu initial brightening (2124:50 UT) and the poleward expansion (2127:50 UT).
In contrast, this two-stage development was not evident in the global images, where the onset brightening started at 2127:49 UT.
Thus, the onset in global images was not simultaneous with the Akasofu initial brightening but rather with the poleward expansion in the all-sky images.
The Akasofu initial brightening was not observed in the global images, which may possibly be attributed to the limited spatial resolution of global images for thin auroral arc brightenings. These comparisons suggest that the substorm onset identified in global images does not correspond directly to the Akasofu substorm onset, but rather to the poleward expansion.
|(1) Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Aichi, 464-8601 Japan.|
|The Importance of Ionospheric Conductivity to Magnetospheric Reconnection Rate and Cross Polar Cap Potential|
|Jensen, J.B., email@example.com (1)|
Raeder, J., firstname.lastname@example.org (1)
Maynard, K., email@example.com (1)
Cramer, W.D., firstname.lastname@example.org (1)
|Using MHD simulations we examined the effect of ionospheric conductivity on the dynamics of the magnetosphere. Using OpenGGCM we modeled two events, a storm period March 17, 2013 and a calmer period May 4, 2005. We studied the changing conductivity due to precipitation by changing the number of incoming electrons by several orders of magnitude. We found that as precipitation increased an order of magnitude the Cross Polar Cap Potentials(CPCP) decreased by 30%. Increasing the precipitation an order of magnitude also caused the subsolar magnetopause location to move earthward, up to 0.5 earth radius. It appears from initial analyses that the reconnection rate is not affected significantly by the changes to ionospheric conductivity. This raises some possible issues as the CPCP has been considered a good approximation for the reconnection rate. The CPCP depends heavily on the ionospheric conductivity due to precipitation, and in our simulations it appears the reconnection rate is not so dependant. The possible discrepancies in matching CPCP to reconnection rate could arise from viscous interaction and polar cap saturation. When the ionosphere has lower conductivity viscous interactions can be significant and can cause the CPCP to be higher than the reconnection rate. When the ionosphere is in a higher conductivity state the polar cap may become saturated and the CPCP doesn't rise higher. In our simulations, preliminary analysis appears to show that the reconnection rate potential of the magnetosphere does not saturate, but it is the potential in the polar caps that saturates resulting in a higher reconnection rate than CPCP.
|(1) Space Science Center, University of New Hampshire, Durham New Hampshire, 03823|
|Recent progress in the understanding of the substorm onset instability|
|Kalmoni,N.M.E., email@example.com (1)|
Rae, I.J., firstname.lastname@example.org (1)
Murphy, K.R., email@example.com (2)
Forsyth, C., firstname.lastname@example.org (1)
Watt, C.E.J., email@example.com (3)
Samara, M., firstname.lastname@example.org (2)
Michell, R.G., email@example.com (2)
Grubbs, G., firstname.lastname@example.org (2)
Yeoman, T.K., email@example.com (4)
Owen, C.J., firstname.lastname@example.org (1)
Fazakerley, A., email@example.com (1)
|Recent work has highlighted that exponentially growing periodic features, nicknamed ‘auroral beads', form longitudinally along the substorm onset arc, indicating the action of a plasma instability. Since the substorm onset arc lies on closed magnetic field lines, this demonstrates that the instability exists in the near-Earth magnetotail, Earthward of the tail reconnection site. |
We conduct a statistical study of independently identified substorm onset arcs to identify any characteristic spatial scales present along the substorm onset arc. In contrast to the prevailing assumption that auroral beads are a special case phenomenon, we show that they are present along the vast majority of substorm onset arcs. These beads have significantly smaller amplitudes relative to the background auroral arc, making them invisible to the eye without such quantitative analyses. This reveals that auroral beads are highly likely to be ubiquitous to all onset arcs.
Our results statistically show that these auroral beads grow exponentially through onset, with growth commencing prior to the large-scale exponential growth of auroral intensity typically associated with auroral substorm onset. We thus conclude that a magnetospheric plasma instability on closed field-lines is fundamental to the release of stored energy in the magnetotail during substorms.
Finally, we utilise multispectral observations of a substorm onset arc to further understand the auroral acceleration processes driving auroral beads. Together with in-situ measurements, we discuss the potential magnetospheric drivers of periodic perturbations of the substorm onset arc.
|(1) Mullard Space Science Laboratory, University College London, Dorking, UK|
(2) NASA GSFC, Greenbelt, MD, USA
(3) Department of Meteorology, University of Reading, Reading, UK
(4) Department of Physics and Astronomy, University of Leicester, Leicester, UK
|Forces acting on the bursty bulk flow plasma - Cluster and MMS results|
|Karlsson, T., firstname.lastname@example.org (1)|
Lindqvist, P.-A., email@example.com (1)
Kullen, A., firstname.lastname@example.org (1)
|The fate of bursty bulk flows (BBFs) as they reach the inner magnetosphere is unclear. To understand the BBF dynamics in the inner tail, we need to know what forces act on the BBF plasma. The relation between the magnetic (jxB) and thermal plasma pressure forces (-grad p) determines if that plasma is accelerated or braked. With Cluster multi-point measurement the magnetic force was determined for 67 BBF events. It was shown that the magnetic tension force was consistently directed towards Earth, whereas the magnetic pressure gradient force increased in magnitude closer in to Earth, and was all the time directed tailwards. This resulted in a net acceleration for X_GSE < -14 R_E, while the magnetic force braked the plasma closer to Earth. Since the magnetic pressure gradient could not be determined locally, this result was a step towards understanding the dynamics, but an incomplete result. With the high-quality MMS particle data it is possible to determine the local plasma pressure gradient, and add an important piece of the puzzle. We will present examples of the full force balance between pressure and magnetic forces on a number of BBF events in the inner magnetosphere. A third factor may also important in determining the BBF dynamics: radiation losses from plasma wave emissions. We will show some preliminary estimates of the importance of this effect.
|(1) Space and Plasma Physics, School of Electrical Engineering, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden|
|The Substorm Current Wedge|
|Kepko, L., email@example.com|
|Over 40 years ago the concept of the substorm current wedge (SCW) was developed to explain the pattern of magnetic signatures observed on the ground and in geosynchronous orbit during the substorm expansion phase. The ensuing decades saw advancements in our understanding of this system from new observations, including radar and low-altitude spacecraft, theoretical considerations, and MHD simulations, and the SCW remains a guiding paradigm on the large scale to this day. Although the line current model of the SCW broadly explains the general characteristics and patterns of magnetic perturbations observed on the ground, recent work has necessitated a need to modify this picture, and there still remain major open questions. A principal alteration is the inclusion of a Region-2 sense current earthward of the traditional SCW, which has support in MHD simulations and some observational support. And while the substorm current wedge (SCW) is able to represent the large scale characteristics of this couple system, it represents an integration of many small scale current systems. The relationship between small-scale, filamented currents observed in the magnetosphere and the larger current system is not well understood. In this paper I review the current state of understanding of this important piece of MI coupling, including new results from MMS.
|(1) NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA|
|Magnetotail fast flow occurrence rate and dawn-dusk asymmetry at X ~ -60 RE|
|Kiehas, S. A., firstname.lastname@example.org (1)|
Runov, A., email@example.com (2)
Angelopoulos, V., firstname.lastname@example.org (2)
Hietala, H., email@example.com (2)
|We use five years (2011-2015) of 3 ARTEMIS data to statistically investigate earthward and tailward flows at around 60 RE downtail.|
This magnetotail region near lunar orbit has rarely been visited by spacecraft in the past and most flow observations with a broader data range were made within X < - 50 RE. We find that a significant portion of fast flows is directed earthward. Depending on the flow speed, the earthward directed flows contribute by 43 % (vx > 400 km/s) to 56 % (vx > 100 km/s) to the observed flows. Considering only the flow component perpendicular to the magnetic field, the portion of earthward flows reduces to about 29% (vx > 400 km/s) to 44% (vx > 100 km/s). As expected, earthward (tailward) flows are predominantly accompanied with positive (negative) Bz. A dawn-dusk asymmetry in the flow occurrence is seen with about 60% of tailward flows occurring in the dusk sector. For earthward flows, the situation is less clear, with 43% (vx > 100 km/s) to 53% (vx > 400 km/s) occurring in the dawn sector. Considering only the flow component perpendicular to the magnetic field, earthward flows with v⊥x < 400 km/s are nearly symmetrically distributed over the dawn and dusk sectors, but 58% of earthward flows with v⊥x > 400 km/s occur in the dusk sector.
|(1) IWF, ÖAW, Graz, Austria|
(2) EPSS, UCLA, Los Angeles, USA
|What makes auroral arcs and how do they relate to the inner magnetosphere?|
|Knudsen, D.J., firstname.lastname@example.org (1)|
Lysak, R.L., email@example.com (2)
|The visible aurora can be understood as a coupled system that includes a magnetospheric "generator" at altitudes above ~2 RE; the M-I coupling medium, in which auroral acceleration takes place; and the base in the ionosphere-thermosphere, which is important both electrodynamically, and as the region in which the optical emissions occur. Perhaps unsurprisingly, the I-T and M-I coupled regions are best understood, due to an extensive set of remote and in-situ observations collected over many decades. To date, however, there is no generally-accepted, self-consistent model of the magnetospheric generator, yet there is significant evidence to indicate that this is where overall auroral morphology is imposed. For example, quiet auroral arcs are known to align with lines of constant geomagnetic latitude to within just a few degrees over many hours of local time. |
At intermediate and small scales, the connection between auroral features and physical mechanisms is better understood. We may distinguish 3 different classes of aurora: the diffuse aurora, the discrete "inverted-V" aurora characterized by a peak in the electron distribution, and the Alfvénic aurora associated with a broad electron energy distribution. The diffuse aurora, caused by both electron and ion precipitation, is associated with the pitch angle scattering of particles due to wave-particle interactions or, especially in the case of ions, with scattering due to the curvature of highly extended magnetic field lines. The inverted-V discrete aurora is generally associated with the formation of a quasi-static potential drop, accelerating electrons downward and ions upward. This can be associated with the formation of double layers, localized regions in which quasi-neutrality is violated leading to strong parallel electric fields. The Alfvénic, or broadband aurora is often assumed to form by the rapid fluctuation (on 1-second time scales) of the parallel electric field, likely due to the reflections of Alfvén waves in the ionospheric Alfvén resonator, although some models associate it with the entrance of electrons at various altitudes gaining a varying degree of acceleration. The inverted-V and Alfvénic auroras are associated with the generation of quasi-static or time-varying field-aligned currents, and the processes that generate these currents, together with the interactions and feedback from the ionosphere, will determine the structure and appearance of these types of aurora.
This discussion will attempt to delineate the known and unknown elements of auroral physics, with a view toward pathways to a eventual, complete understanding of the auroral system.
|(1) Department of Physics and Astronomy, University of Calgary, Calgary, AB, Canada|
(2) School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA
|Substorm-associated radio emissions: Direction-finding and fine-structure observations|
|LaBelle, J., firstname.lastname@example.org (1)|
|Auroral radio emissions associated with polar substorms include impulsive and continuous auroral hiss, AKR, MF-burst, and 2fce, 3fce, and 4fce auroral roar. Of these, impulsive hiss and MF-burst turn on promptly at substorm onset, have typical durations of minutes, and have potential to serve as substorm onset timing indicators. Auroral hiss is believed to arise from coherent amplification of whistler mode noise by the enhanced precipitating auroral electron beam. LF hiss at frequencies up to 1 MHz must originate below 1000 km in the ionosphere, where the gyrofrequency is above 1 MHz. The MF-burst generation mechanism is unknown, though generation in the topside from mode converted electron plasma waves has been suggested, with the latter waves generated by the auroral electron beam. The temporal correlation between MF-burst and LF-hiss would arise naturally if they are excited by the same auroral electron beam, although this raises the question of how the two emissions manage to tap the same energy source. If the energy for both MF-burst and hiss emissions comes ultimately from the same auroral electron beam, their close temporal correlation would explained, and a spatial correlation would similarly be predicted, but it raises the question of how the two emissions manage to tap the same energy source. In the last couple of years, instruments at Toolik Lake, Alaska, have provided simultaneous observations of LF-hiss and MF-burst fine structure. The latter shows greater complexity than previously reported in the literature, and the combination may provide hints about how the emissions share the energy available in the precipitating electrons. Also in the last couple of years, an antenna array operated at Sondrestrom, Greenland, has provided many examples of simultaneous direction-finding measurements of LF-hiss and MF-burst, in some cases simultaneous with incoherent scatter radar measurements of ionospheric density profiles. These data enable the spatial correlation of the two emissions to be probed. Furthermore, the successful direction-finding of these emissions suggests a method for confirming hemispherical asymmetries in substorm onsets under extreme IMF-By conditions by using antenna arrays located in approximately magnetically conjugate observatories.
|(1) Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire, 03755 USA|
|Variability in the Pedersen conductance associated with substorms using all-sky camera and incoherent scatter radar data|
|Lam, M. M., email@example.com (1)|
Jackman, C. M., C.Jackman@soton.ac.uk (1)
Reimer, A., firstname.lastname@example.org (2)
Varney, R., email@example.com (2)
Freeman, M. P., firstname.lastname@example.org (3)
Rae, I. J., email@example.com (4)
Kalmoni, N. M. E., firstname.lastname@example.org (4)
Forsyth, C., email@example.com (4)
Sandhu, J., firstname.lastname@example.org (4)
|The variability of energy released by a substorm is not well understood, in part because of the observational challenges associated with the partitioning of the released energy between Earth and Space. An important component of the released energy is Joule Heating of the atmosphere, which depends on the product of the ionospheric Pedersen conductance ΣP and the square of the electric field in the rest frame of the neutral atmosphere. The most accurate specification of ΣP is obtained using incoherent scatter radar (ISR) observations of electron density and modelled values of particle collision frequencies. However the limited field of view of an ISR means that this method cannot be used to estimate conductance over the relatively large spatial extent of the substorm Joule heating region. To overcome this, Kosch et al. (1998) found a relationship between localized EISCAT ISR-derived conductances and co-located auroral intensities I at 557.7 nm measured by a ground-based camera. Their aim was to allow ΣP to be inferred over the much wider field of view of any camera(s). Here we use the existence of a relationship between ΣP and I to exploit the 20 THEMIS All-Sky Imagers (ASIs) deployed across Canada in order to estimate the continental scale ΣP associated with substorms. We first test and refine the Kosch et al. relationship using co-located data from the THEMIS Fort Yukon ASI and the Poker Flat Advanced Modular ISR (PFISR). The PFISR data were collected during the PFISR Ion-Neutral Observations in the Thermosphere (PINOT) Campaign in November 2012 and March 2013. Using the Substorm Onsets and Phases from Indices of the Electrojet (SOPHIE) method, we identified 37 substorm events observable to the THEMIS ASI network between 2006 and 2014 using the necessary auroral measurements from the THEMIS ground-based observatory (GBO) network of ASIs and magnetometers. The I to ΣP conversion is used to estimate the variation in ΣP in different phases of the substorm cycle. Joule Heating loss in the ionosphere during the substorm is a critical missing aspect of the current substorm energy budget.
|(1) Space Environment Physics Group, University of Southampton, Southampton, SO17 1BJ, UK.|
(2) Center for Geospace Studies, SRI International, Menlo Park, California, USA.
(3) British Antarctic Survey, Cambridge, CB3 0ET, UK.
(4) Mullard Space Science Laboratory, University College London, Dorking, RH5 6NT, UK
|Examining Energetic Particle Injections During Substorm Activity and the Effects on the Inner Magnetosphere|
|Leonard, T. W., email@example.com (1) |
Jaynes, A. N., firstname.lastname@example.org (1)
Baker, D. N., email@example.com (1)
Blake, J. B., firstname.lastname@example.org (2)
Burch, J. L., email@example.com (3)
Cohen, I. J., firstname.lastname@example.org (4)
Ergun, R. E., email@example.com (1)
Fennell, J. F., firstname.lastname@example.org (2)
Gershman, D. J., email@example.com (5)
Giles, B. L., firstname.lastname@example.org (5)
Le Contel, O., email@example.com (6)
Mauk, B. H., firstname.lastname@example.org (4)
Russell, C. T., email@example.com (7)
Strangeway, R. J., firstname.lastname@example.org (7)
Torbert, R. B., email@example.com (8)
Turner, D. L., firstname.lastname@example.org (2)
Wilder, F. D., email@example.com (1)
|The Magnetospheric Multiscale (MMS) Fly's Eye Energetic Particle Spectrometer (FEEPS) instrument has observed a multitude of particle injection events since its launch in 2014. These injections often lead to enhancements observed by the Van Allen Probes MagEIS instrument, as well as other elements of the modern-day Heliophysics System Observatory. The high spatial resolution and unprecedented time scales of the MMS observations provide a microscope view of the plasma physical properties in Earth's neighborhood while the combination with other missions in the Heliophysics System Observatory provides a telescope view of the larger Sun-Earth system. Past studies have found a relationship between substorm activity, which can be more powerful during high speed solar wind stream events, and enhancements of the outer radiation belt electrons. In this study, we examine several distinct particle injection events with dipolarization front characteristics observed by MMS and multiple complementary missions. In particular, cases involving multiple injection events are compared to singular injection events for their effectiveness of creating radiation belt enhancements.
|(1) Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, Colorado, USA|
(2) Space Sciences Department, The Aerospace Corporation, El Segundo, California, USA
(3) Southwest Research Institute, San Antonio, Texas, USA
(4) The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
(5) NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
(6) Laboratoire de Physique des Plasmas, CNRS/Ecole Polytechnique/UPMC/P11, Vélizy, France
(7) Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA
(8) Space Science Center, University of New Hampshire, Durham, New Hampshire, USA
|Proton auroras during the transitional stage of substorm onset|
|Liang, J., firstname.lastname@example.org (1)|
Donovan, E., email@example.com (1)
Spanswick, E., firstname.lastname@example.org (1)
Hampton, D., email@example.com (2)
|Optical auroral measurements repeatedly reveal that there is often a ~1-2 minute transitional stage between a quiescent preexisting arc and the significant auroral expansion. Such a transitional stage is characterized by a gradual intensification and in many cases the emergence of azimuthally-spaced auroral structures, aka the auroral beads, along the preexisting arc. However, the above-depicted auroral dynamics are pertinent to electron auroras which are dominant in auroral luminosity, yet the variation of proton auroras associated with the transitional stage of substorm onset is much less known. In this study, we use proton auroral measurements from the FESO instrument at Athabasca and the Meridian Spectrograph at Poker Flat, and collect events when the proton auroral measurements cover the initial onset beading sector of electron auroras observed by THEMIS/Rainbow all-sky imagers. Our major results include: (1) we confirm the previous notion that the onset electron auroral arc is usually located at the poleward "shoulder" of the preexisting proton auroral band. (2) While the electron aurora typically features an overall exponential intensification during the transitional stage, the proton auroral intensity at the same location as, and equatorward of, the onset electron auroral arc, generally shows no clue of intensification during the transitional stage. Instead, in some cases the preexisting proton aurora tends to slightly fade at the first minute of the transitional stage. Substantial intensification and expansion of proton auroras occur concurrently with or after the start of the poleward expansion of electron auroras. The above observations on proton auroras during the transitional stage of electron auroral breakup shed implications and constraints on the possible mechanisms of substorm onset. More specifically, we suggest that there is no significant ion energization or large-scale magnetic field reconfiguration during the initial stage of the substorm onset.
|(1) Department of Physics & Astronomy, University of Calgary, Alberta, Canada|
(2) Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, USA
|Collisionless magnetic reconnection rate: Implications for the time-scale of energy release during magnetospheric substorms|
|Liu, Y. -H., Yi-Hsin.Liu@Dartmouth.edu (1)|
Hesse, M., firstname.lastname@example.org (2)
Cassak, P. A., email@example.com (3)
Birn, J., firstname.lastname@example.org (4)
Shay, M., email@example.com (5)
Guo, F., firstname.lastname@example.org (6)
Daughton, W., email@example.com (6)
Li, H., firstname.lastname@example.org (6)
|The magnetic energy built-up in the stretched dipole field at Earth's nightside can be rapidly released via magnetic reconnection, driving geomagnetic substorms near Earth. The rate at which the reconnection diffusion region processes the inflowing magnetic flux can be quantified by the inflow speed normalized by the Alfven speed, which characterizes the reconnection jet. Observations and numerical simulations reveal that essentially collisionless magnetic reconnection of a thin current sheet in the steady state tends to proceed in a similar rate of order 0.1, independent of dissipation mechanism or physical model. However, the explanation of this value has remained unclear for decades. We propose a model that provides insight to this longstanding problem. The prediction from this model compares favorably to particle-in-cell simulations of magnetic reconnection in both the non-relativistic and extremely relativistic limits. The importance of these results is not limited to magnetospheric substorms, but also has applications to solar, magnetically confined fusion, and astrophysical settings.
|(1) Dartmouth College, NH, USA|
(2) University of Bergen, Bergen, Norway
(3) West Virginia University, WV, USA
(4) Space Science Institute, CO, USA
(5) University of Delaware, DE, USA
(6) Los Alamos National Laboratory, NM, USA
|Sawtooth events and plasma sheet O+: CME- and SIR-driven events|
|Lund, E.J., Eric.Lund@unh.edu (1,2)|
Nowrouzi, N., email@example.com (1,3)
Kistler, L.M., Lynn.Kistler@unh.edu (1,3)
Cai, X., firstname.lastname@example.org (4,5)
Liao, J., email@example.com (1)
|The role of ionospheric ions in sawtooth events is an open question. Simulations[A,B,C] suggest that O+ from the ionosphere produces a feedback mechanism for driving sawtooth events. However, observational evidence[D,E] suggest that the presence of O+ in the plasma sheet is neither necessary nor sufficient. In this study we investigate whether the solar wind driver of the geomagnetic storm has an effect on the result. Building on an earlier study[D] that used events for which Cluster data is available in the plasma sheet, we perform a superposed epoch analysis for coronal mass ejection (CME) driven storms and streaming interaction region (SIR) driven storms separately, to investigate the hypothesis that ionospheric O+ is an important contributor for CME-driven storms but not SIR-driven storms[B].|
[A]O. J. Brambles et al. (2011), Science 332, 1183.
[B]O. J. Brambles et al. (2013), JGR 118, 6026.
[C]R. H. Varney et al. (2016), JGR 121, 9688.
[D]J. Liao et al. (2014), JGR 119, 1572.
[E]E. J. Lund et al. (2017), JGR, submitted.
|(1) Space Science Center, University of New Hampshire, Durham, NH 03824, USA|
(2) College Brook Scientific, Durham, NH 03824, USA
(3) Physics Department, University of New Hampshire, Durham, NH 03824, USA
(4) Bradley Department of Electrical and Computer Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
(5) Langley Research Center, National Aeronautics and Space Administration, Hampton, VA 23681, USA
|Stormtime Substorms: Occurrence Features and Flow Channel Triggering|
|Lyons, L.R., firstname.lastname@example.org (1)|
Zou, Y., email@example.com(2)
Nishimura, Y., firstname.lastname@example.org(1.2)
Gallardo-Lacourt, B.. email@example.com (3)
E. F. Donovan, E.F., firstname.lastname@example.org (3)
Angelopoulos, V., email@example.com (4)
|Storms represent an excellent opportunity for using all-sky-imager (ASI) observations to study the occurrence and flow channel triggering of substorms. Despite other activity, substorm onset identifications are quite clear and distinguishable from other activity via equatorward arc brightening followed by poleward expansion (i.e., the standard Akasofu substorm definition). Furthermore, pre-onset streamer identification is often clearer than for non-storm times due to emission intensity, so identification of consistency with flow channel triggering is facilitated. We have examined 9 CME and 10 high-speed stream storms (HSS) storms with nightside main phases over North America and with good viewing with the THEMIS ASI array. We require that previous substorm activity fade before a new substorm onset is identified, but we do not invoke a minimum time separation between onsets. We find that substorms occur ~2-3 times more often for HSS storms (which have strongly fluctuating IMF) than for steady southward IMF periods that occur during CME storms. We find that pre-onset streamers consistent with triggering by pre-onset flow channels are seen clearly for over 90% of over 60 identified onsets with initial arc brightening fully within the field-of-view of the imager array. Most of the streamers are "tilted" streamers that tilt equatorward as they extent a considerable distance in the dawnward direction. Equatorward motion of the tilted streamers is commonly seen until the equatorward most edge of the streamer approaches the MLT and latitude of the onset. The equatorward motion of these streamers can be traced over as much as several degrees of latitude from the auroral poleward boundary and for time intervals prior to onset as long as ~35 min. Connections to polar cap flow channels will also be considered to the extend that relevant observations are available.
|(1) Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, USA.|
(2) Department of Electrical and Computer Engineering and Center for Space Physics, Boston University, Boston, Massachusetts, USA
(3) Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada.
(4) Department of Earth, Planetary and Space Science, University of California, Los Angeles, California, USA.
|Toward a unified model of substorm|
|Machida, S., firstname.lastname@example.org (1)|
Fukui, K., email@example.com (1)
Miyashita, Y., firstname.lastname@example.org (2)
Ieda, A., email@example.com (1)
|Numerous models of substorms have been proposed so far, and they are roughly divided into two categories, i.e., the outside-in category that is represented by the near-Earth neutral line (NENL) model and the inside-out category that is represented by the current disruption model or the ballooning instability model. Controversies have been raised for many years over the validity of those models. However, in recent years we have obtained important clues to solve this long-standing issue by analyzing THEMIS probe data for substorms and pseudo-substorms separately. [Fukui et al., 2017]|
The key is the plasma pressure in the equatorial region, and it was about 1.3 times higher in substorms, than the pseudo-substorm in the region between X ~ -7 and -8 Re. However, no difference was found beyond X ~ -10 Re. Therefore, the spatial gradient of the plasma pressure in the region of X ~ -7.5 Re must be a necessary condition for the occurrence of substorm. Abrupt earthward flows originated from the catapult current sheet relaxation and subsequent magnetic reconnection at the NENL just prior to the onset is a common signature for both substorm and pseudo-substorm. Those flows must initiate some instability, possibly the ballooning instability around the flow braking region.
Substorms do not occur only with the magnetic reconnection. If there is enough plasma pressure gradient, the system can develop into a substorm. Otherwise, it will end up with a pseudo-substorm. We emphasize that both NENL model and the ballooning instability model are partially correct but incomplete, and the true model of substorm can be constructed by synthesizing multiple models of substorm including at least these two.
|(1) Institute for Space-Earth Environmental Research, Nagoya University , Nagoya, Aichi, 464-8601 Japan|
(2) Korea Astronomy and Space Science Institute, Daejeon, Republic of Korea
|A Comparison of Ground Observations of the Substorm Current Wedge to the Predictions of a Global MHD Simulation|
|McPherron, R.L., firstname.lastname@example.org (1)|
Mostafa El Alaoui, email@example.com (2)
|A characteristic feature of a substorm as recorded on the ground at midlatitudes is the substorm current wedge. The current wedge is seen as a systematic pattern in the X and Y components of the perturbation magnetic field. The change in the X component has a positive maximum at the center of the wedge that falls off with distance becoming negative well outside the wedge. The Y component is a maximum under the upward current and a minimum under the downward current of the wedge. For a symmetric wedge the zero crossing in the profile of changes in Y is at the center of the wedge. We have extensively analyzed a substorm on March 14, 2008 for which we have observations from five THEMIS spacecraft located beyond 10 Re near 2100 local time. The available data include an extensive network of all sky cameras and ground magnetometers that establish the times of various auroral and magnetic events. We have determined the location and strength of several current wedges during an 8-hour interval. We have also investigated this interval with a global MHD simulation. We find that the simulation responds with a sequence of fast flows and dipolarization events in the same way as seen in the data, but not at the precisely the same times or same locations as observed. We have identified expansion onsets in the simulation and will create a time sequence of profiles of changes in the X and Y components as predicted by the simulation. We will compare these to the patterns observed in the data. Typically the simulation shows complex reconnection and flow activity in the tail but seldom are more than two flow channels present simultaneously. The channels follow tortuous paths that are often reflected or deflected before arriving at the outer magnetosphere. We will study the relation of gradients in plasma pressure and flux tube volume created by the flows to the current wedges predicted by the simulation.
|(1) Department of Earth, Planetary, and Space Sciences, University of California Los Angeles, CA 90095-1567|
(2) Department of Physics and Astronomy, University of California Los Angeles, CA 90095-154705
|A Dialog Discussing whether the Substorm is a Fundamental Mode of Response of the Magnetosphere|
|McPherron, R. L., firstname.lastname@example.org (1)|
Ohtani, S., email@example.com (2)
|A substorm is a coherent response of the magnetosphere to fluctuations in the solar wind driver. It is a fundamental mode of response in which the shape of the magnetosphere, the properties of the plasma sheet, the electrical connection of the magnetosphere to the ionosphere, the aurora, and ground magnetic activity all behave in consistent and repeatable manner. This response exhibits two dominant frequencies: the most obvious is a tendency to occur at a separation of ~180 minutes; less obvious is a recurrence period of about 30-40 minutes. Substorms typically occur 2-10 times per day with a long-term average of about 4.5 per day. Their occurrence is modulated by season and the solar cycle. Ensemble averages of various substorm indicators show the "typical" .substorm is structured into three phases: a 50 min growth phase, a 30 min expansion phase, and a 90 min recovery phase. Most substorms have multiple onsets or intensifications of the expansion phase. The onset of the substorm expansion is often confused by pseudo breakups which are short duration events that do not develop into a full expansion. The expansion and recovery phases are structured by poleward boundary intensifications of the aurora followed by auroral streamers moving to lower latitudes. These features are lost in ensemble averages. During steady moderate driving the magnetospheric response transitions to another fundamental response mode called steady magnetospheric convection in which auroral expansions disappear. If driving is very strong a third response mode develops in which the substorm mode reappears but on a much more global scale encompassing the entire nightside.
|(1) Department of Planetary, Earth, and Space Sciences, University of California Los Angeles, Los Angeles, CA, 90095-1567|
(2) The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA.
|Energization of the Ring Current through Convection of Substorm Enhancements of the Plasma Sheet Source|
|Menz, A.M, firstname.lastname@example.org (1)|
Kistler, L.M., email@example.com (1)
Mouikis, C.G., firstname.lastname@example.org (1)
Spence, H.E., email@example.com (1)
Henderson, M.G., firstname.lastname@example.org
Matsui, H., email@example.com (1)
|It has been shown that electric field strength and night-side plasma sheet density are the two best predictors of the adiabatic energy gain of the ring current during geomagnetic storms (Liemohn and Khazanov, 2005). While H+ dominates the ring current during quiet times, O+ can contribute substantially during geomagnetic storms. Substorm activity provides a mechanism to enhance the energy density of O+ in the plasma sheet during geomagnetic storms, which is then convected adiabatically into the inner-magnetosphere. Using the Van Allen Probes data in the the plasma sheet source region (defined as L>5.5 during storms) and the inner magnetosphere, along with LANL-GEO data to identify substorm injection times, we show that adiabatic convection of O+ enhancements in the source region can explain the observed enhancements in the inner magnetosphere. We use the UNH-IMEF electric field model to calculate drift times from the source region to the inner magnetosphere to show how enhancements in the inner-magnetosphere can be explained by enhancements in the plasma sheet source many hours before.
|(1) University of New Hampshire, Durham, New Hampshire, USA|
(2) Los Alamos National Labs, Los Alamos, New Mexico, USA
|Magnetotail stability in the global context inferred from MHD simulations|
|Merkin, V. G., firstname.lastname@example.org (1)|
Garcia-Sage, K., email@example.com (2)
Sitnov, M., Mikhail.Sitnov@jhuapl.edu (1)
Moore, T. E., firstname.lastname@example.org (2)
Pembroke, A. D., email@example.com (2)
|Recent results on the theory of magnetotail stability suggest that certain magnetotail configurations may have a potential for tearing instability which eventually leads to the change in magnetic topology, i.e., reconnection. The necessary condition for the instability is a tailward Bz gradient or a region of magnetic flux accumulation (a Bz hump). However, such configurations are notoriously difficult to infer from observations and may additionally be interchange unstable in 3D. In order to understand the conditions and possibility of formation of such configurations in a realistic global context, we compute tearing and interchange magnetotail stability parameters in global magnetohydrodynamic (MHD) simulations of the magnetosphere. We demonstrate the formation of persistent regions of magnetic flux accumulation in the simulated magnetotail and discuss their relationship with bursty flows, low entropy channels and tearing and interchange instabilities. These processes are also mapped into the ionosphere and their auroral signatures are additionally discussed. These results are particularly timely as they provide important global context for MMS observations as the mission traverses the night side magnetosphere.
|(1) The Johns Hopkins University Applied Physics Laboratory, Laurel, MD|
(2) NASA Goddard Space Flight Center, Greenbelt, MD
|A case study of magnetotail conditions at substorm and pseudosubstorm onsets|
|Miyashita, Y., firstname.lastname@example.org (1)|
Angelopoulos, V., email@example.com (2)
Fukui, K., firstname.lastname@example.org (3)
Machida, S., email@example.com (3)
|While a substorm involves initial brightening and growth of wave-like structure of the auroral onset arc and the subsequent auroral poleward expansion, a pseudosubstorm (pseudobreakup) involves only the first two steps of auroral development and subsides without poleward expansion. To understand what makes this difference, we studied magnetotail conditions at a pseudosubstorm onset and the subsequent substorm onset, using multipoint THEMIS data. In the present event, magnetic reconnection occurred tailward of X~-22 Re and near X~-17 Re before initial brightening of the pseudosubstorm and the substorm, respectively. In the near-Earth magnetotail at X~-10 Re, the plasma beta, ion pressure, and radial pressure gradient were smaller and magnetic field lines were less stretched at the pseudosubstorm onset than at the substorm onset. Dipolarization (persistent net increase in the northward magnetic field) did not occur for the pseudosubstorm, whereas it began simultaneously with poleward expansion for the substorm. These observations suggest that conditions of the near-Earth magnetotail possibly affect whether the initial action develops into a full-fledged substorm.
|(1) Korea Astronomy and Space Science Institute, Daejeon, South Korea|
(2) Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, USA
(3) Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan
|Arase (ERG) Project|
|Miyoshi, Y., firstname.lastname@example.org (1)|
Shinohara, I., email@example.com (2)
Takashima, T., firstname.lastname@example.org (2)
Asamura, K., email@example.com (2)
Shiokawa, K., firstname.lastname@example.org (1)
Higashio, N., email@example.com (2)
Mitani, T., firstname.lastname@example.org (2)
Kasahara, S., email@example.com (3)
Yokota, S., firstname.lastname@example.org (2)
Kazama, Y., email@example.com (4)
Wang, S.-Y., firstname.lastname@example.org (4)
Kasahara, Y., email@example.com (5)
Kasaba, Y., firstname.lastname@example.org (6)
Yagitani, S., email@example.com (5)
Matsuoka, A., firstname.lastname@example.org (2)
Kojima, H., email@example.com (7)
Katoh, Y., firstname.lastname@example.org (6)
Hikishima, M., email@example.com (2)
Seki, K., firstname.lastname@example.org (3)
Hosokawa, K., email@example.com (7)
Ogawa, Y., firstname.lastname@example.org (8)
Oyama, S., email@example.com (1)
Kuita, S., firstname.lastname@example.org (1)
ERG Project Team
|The ERG (Exploration of energization and Radiation in Geospace) is a geospace exploration project. The project focuses on the geospace dynamics in the context of the cross-energy coupling via wave-particle interactions. The project consists of the satellite observation team, the ground-based network observation team, and integrated-data analysis/simulation team. The Arase (ERG) satellite was launched in December, 2016. Comprehensive instruments for plasma/particles, and field/waves are installed in the ERG satellite to understand the cross-energy coupling system. In the ERG project, several ground-network teams join; magnetometer networks, radar networks, optical imager networks, etc. Moreover, the modeling/simulations play an important role for the quantitative understanding. In this presentation, we will talk about an overview of the Arase (ERG) project and brief overview of the campaign observations in spring 2017 that focused on the chorus-wave particle interactions and the pulsating aurora.
|(1) ISEE, Nagoya University, Nagoya 464-8601, Japan|
(2) JAXA, Sagamihara 252-0522, Japan
(3) University of Tokyo, Tokyo 113-8654, Japan
(4) ASIAA, No.1, Sec. 4, Roosevelt Rd,Taipei, Taiwan
(5) Kanazawa University, Kanazawa 920-1192, Japan
(6) Tohoku University, Sendai 980-8578, Japan
(7) RISH, Kyoto Univ, Uji 611-0011, Japan
(8) NIPR, Tachikawa 190-0014, Japan
|Forecasting substorm activity with global MHD and the Minimal Substorm Model|
|Morley, S.K., email@example.com (1)|
Haiducek, J.D., firstname.lastname@example.org (2)
Welling, D.T., email@example.com (2)
|Magnetospheric substorms can be considered analogous to earthquakes; energy from the solar wind is transferred into Earth's magnetosphere and, after a sufficient period of loading, is rapidly released during substorms. Even though substorms represent a common and fundamental mode of magnetospheric response, we cannot currently predict when a substorm will occur, nor can we determine what the magnitude of the substorm will be. A reduced dimensionality model - the Minimal Substorm Model (MSM) - has reproduced observed distributions of inter-substorm timing interval and substorm magnetic bay magnitude. The Space Weather Modeling Framework (SWMF) is the global MHD code running operationally at NOAA's Space Weather Prediction Center, but the ability of global MHD models to reproduce substorm occurrence, timing and magnitude has not been demonstrated. We will present simulations of January 2005 using the SWMF and the MSM, and statistical analyses of their forecast skill. Future directions for improving substorm dynamics in global MHD codes, and for operational forecasting of substorms, will be discussed.
|(1) Los Alamos National Laboratory, Los Alamos, New Mexico|
(2) University of Michigan, Ann Arbor, Michigan
|Response of energetic particles to local magnetic dipolarization inside geosynchronous orbit|
|Motoba, T.M., firstname.lastname@example.org (1)|
|Magnetic field dipolarization and energetic particle injections are distinct phenomena observed in the inner magnetosphere during the substorm expansion phase. Magnetic field dipolarization represents a reconfiguration (relaxation) of the magnetic field topology. Energetic particle injections involve the sudden inward transport of energetic ions and electrons (typically tens to hundreds of keV) from the plasma sheet. Such injected particles are considered to play an important role in building-up Earth's ring current during geomagnetic storms, providing the seed population for the outer radiation belt electrons, and introducing the source population of ions and electrons responsible for the generation and growth of various plasma waves. Compared to a wealth of knowledge about the phenomenology of energetic particle injections and their association with magnetic field dipolarization at/outside geosynchronous orbit (GEO), our understanding of them inside GEO remains incomplete because of a very limited number of previous studies. By statistically examining field and particle data from Van Allen Probes, we will present the responses of injected/preexisting energetic particles to local magnetic dipolarization inside GEO and discuss the mechanism(s) and factors controlling the dynamical behavior of energetic particles.
|(1) The Johns Hopkins University Applied Physics Laboratory|
|HF radar observations of convection and reconnection during non-substorm intervals|
|Mtumela, Z., MtumelaZ@ukzn.ac.za (1)|
|The SuperDARN (Dual Auroral Radar Network) HF radars in the northern and southern hemisphere auroral zone produce global convection maps of ionospheric plasma motion driven by magnetospheric reconnection process. During non-substorm conditions, the interplanetary magnetic field (IMF) tends to be northward, high speed flow associated with reconnection can also be observed on the nightside, mapping to the magnetospheric tail. The high speed flow and the underlying convection patterns depend on IMF By. These events suggest the release of energy and the attainment of high velocity flows without external drivers such as substorms. Assumption of non-substorm intervals were justified by GOES, IMAGE and Pi2 data. The observations are discussed in relation to magnetic reconnection in the magnetotail
|(1) School of Chemistry and Physics, University of KwaZulu-Natal,P/Bag X54001, Durban, 4000, South Africa|
|The dependence of substorm onset on auroral streamers: a quantitative analysis of auroral dynamics during substorms |
|Murphy, K.R., email@example.com (1)|
Sibeck. D.G., firstname.lastname@example.org (2)
Watt, C.E.J., email@example.com (3)
Rae, I.J., firstname.lastname@example.org (4)
Kepko, L., email@example.com (2)
Mann, I.R., firstname.lastname@example.org (5)
Donovan, E.D., email@example.com (6)
|The auroral substorm is a dynamic display characterized by the poleward and azimuthal expansion of an auroral arc following a period of quiescence and equatorward motion. Despite being studied for over half century the auroral substorm remains shrouded in controversy. This controversy centres on the mechanism responsible for releasing solar wind energy stored in the magnetotail and initiating an auroral substorm. Historically this debate revolved around two models, the Near-Earth Neutral Line and Current disruption models. However, with the dense array of ground-based imagers and conjugate magnetospheric observations a third paradigm has been introduced, the auroral streamer paradigm, adding another layer to the substorm controversy. In this study we use the array of THEMIS all sky imagers to present a detailed analysis of 26 isolated substorms from the growth through early expansion phase using newly developed quantitative auroral tracking tools. Our objective is to develop a clear and consistent spatiotemporal description of poleward boundary intensifications, auroral streamers, and the equatorward auroral arc associated with substorm onset. Using quantitative analysis, we determine an occurrence rate for high-speed auroral forms associated with high-speed ionospheric flow channels during the substorm growth phase and determine how many of these auroral forms can be associated with substorm onset. Our new method enables researchers to progress from qualitative towards reproducible quantitative studies of auroral substorms. Less than 20% of the isolated substorms we studied follow the substorm streamer paradigm and less than 50% of substorms show evidence of any auroral streamer during the substorm growth phase. Using robust quantitative analysis and auroral tracking, this work demonstrates that streamers are not a necessary condition nor precursor of substorm onset.
|(1) Department of Astronomy, University of Maryland, College Park MD|
(2) NASA GSFC, Greenbelt MD
(3) Department of Meteorology, University of Reading, Reading, Berkshire, United Kingdom
(4) Mullard Space Science Laboratory, University College London, Holmbury St Mary, Surrey, United Kingdom
(5) Department of Physics, University of Alberta, Edmonton AB
(6) Department of Physics and Astronomy, University of Calgary, Calgary AB
|Near-Earth plasma sheet boundary dynamics during substorm dipolarization|
|Nakamura, R., firstname.lastname@example.org , (1)|
Nagai, T., email@example.com (2)
Birn, J., firstname.lastname@example.org (3)
Sergeev, V. A., email@example.com (4)
Le Contel, O., firstname.lastname@example.org (5)
Varsani, A., Ali.Varsani@oeaw.ac.at (1)
Baumjohann, W., Wolfgang.Baumjohann@oeaw.ac.at (1)
Nakamura, T.K.M., email@example.com (1)
Apatenkov, S., firstname.lastname@example.org (4)
Artemyev, A., Ante0226@yandex.ru (6)
Ergun, R. E., LASP, Bob.Ergun@lasp.colorado.edu, (7)
Fuselier, S. A., email@example.com, (8)
Gershman, D. J., firstname.lastname@example.org, (9)
Giles, B. J., email@example.com, (9)
Khotyaintsev, Y., firstname.lastname@example.org, (10)
Lindqvist, P.-A, email@example.com, (11)
Magnes, W., Werner.Magnes@oeaw.ac.at (1)
Barry Mauk, B., Barry.Mauk@jhuapl.edu (12)
C. T. Russell, C. T., firstname.lastname@example.org, (6)
Singer, H. J., email@example.com (13)
Stawarz, J., firstname.lastname@example.org (14)
Strangeway, R. J., email@example.com (6)
Slavin, J. A., firstname.lastname@example.org (15)
Ian Cohen, I., email@example.com, (12)
Turner, D.L., firstname.lastname@example.org, (16)
|We report large-scale evolution of the dipolarization in the near-Earth plasma sheet during an intense (AL~1000 nT) substorm on August 10, 2016, when multiple spacecraft at radial distances between 4 and 15 RE were distributed in the night-side magnetosphere. The global dipolarization consists of multiple short time (a couple of min) scale Bz disturbances detected by spacecraft distributed over 9 MLT, consistent with the large-scale substorm current wedge (SCW) observed by ground-based magnetometers. The four spacecraft of the Magnetospheric Multiscale (MMS) were located in the southern hemisphere plasma sheet and observed fast flow disturbances associated with multiple dipolarizations. The high time-resolution measurements from MMS enable us to detect the rapid motion of the field structures and the flow disturbances separately. A distinct pattern of the flow and the field disturbance near the plasma boundaries was found. We suggest that a vortex motion created around the localized flows results in another field-aligned current system at the off-equatorial side of the BBF-associated R1/R2 systems as was predicted by MHD simulation of a localized reconnection jet. The observations by GOES and Geotail, which were located in the opposite hemisphere and local time, support this view. We demonstrate that both the processes of Earthward flow braking and that of accumulated magnetic flux evolving tailward are controlling the dynamics also in the boundary region of the near-Earth plasma sheet.
|(1) Space Research Institute, Austrian Academy of Sciences, 8042 Graz, Austria|
(2) Tokyo Institute of Technology, Tokyo, Japan,
(3) Space Science Institute, Boulder, CO 80301, USA
(4)St. Petersburg State University, St. Petersburg, Russia
(5) LPP, CNRS, Observatoire de Paris, F-75252 Paris, France
(6) University of California, Los Angeles, California, USA,
(7) University of Colorado, Boulder, Colorado, USA,.
(8) Southwest Research Institute, San Antonio, Texas, USA,
(9) NASA, GSFC, Greenbelt, MD 20771, USA,
(10) Swedish Institute of Space Physics, Uppsala, 75121, Sweden,
(11) Royal Institute of Technology, Stockholm 10044, Sweden,
(12) Applied Physics Laboratory, Johns Hopkins University, Maryland, USA
(13) NOAA Space Weather Prediction Center, Boulder, Colorado, USA
(14) Department of Physics, Imperial College London, London, UK,
(15) Department of Climate and Space Sciences and Engineering, University of Michigan, Michigan, USA,
(16) Space Sciences Department, Aerospace Corporation, Los Angeles, California, USA
|Conjugate ground-based and magnetospheric observations of auroral finger-like structures using the THEMIS-E and RBSP-A satellites in the dawnside plasma sheet|
|Nishi, Katsuki, email@example.com (1) |
Shiokawa, Kazuo (1)
Spence, Harlan (2)
Funsten, Herb (3)
Hruehauff, Dennis (4)
|The auroral finger-like structures appear in the equatorward of the auroral oval in the diffuse auroral region, and contribute to the auroral fragmentation into patches during substorm recovery phase. We report first conjugate observations of auroral finger-like structures using the THEMIS GBO cameras and the THEMIS satellites, which was located at a radial distance of ~9 Re in the dawnside plasma sheet. The conjugate event was observed at Narsarsuaq (MLAT: 69.3°N), Greenland, at 0720UT-0820UT (0506LT-0606LT) on 17 February 2012. Analysis of the event produced the following observation facts: 1) variation of parallel electron energy fluxes observed by THEMIS-E shows correspondence to the auroral intensity variation, 2) plasma pressure and magnetic pressure fluctuate in anti-phase with time scales of 5-20 min, 3) perpendicular ion velocity is very small (less than 50 km/s). The second fact is consistent with the idea that the finger-like structures are caused by a pressure-driven instability in the balance of plasma and magnetic pressures in the magnetosphere. Then we also searched simultaneous observation events of auroral finger-like structures with the RBSP satellites which have an apogee of 5.8 Re in the inner magnetosphere. The best event that we found is observed at Gillam, Canada, at ~0900 UT on 14 Nov. 2014. According to the field-line mapping using the Tsyganenko-01 magnetic field model, the footprints of the RBSP-A satellite passed across the auroral finger-like structures several times. We obtained observational facts from this simultaneous observation event as: 1) both electron and ion OMNI fluxes measured by HOPE increase at ~0900 UT as the satellite footprint was getting into the auroral region; 2) chorus wave activities at ~1 kHz measured by EMFSIS enhanced after 0900 UT; 3) absolute value of magnetic pressure is almost ten times larger than that of ion thermal pressure; 4) variation of magnetic pressure and ion thermal pressure are seen in various time scales, including ~5 min which is the time scale of crossing of finger-like structures. In the presentation, we will discuss these observations in the context of magnetospheric instabilities that can cause auroral finger-like structures.
|(1) Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan|
(2) Institute for the Study of Earth, Oceans, and Space, Univ. of New Hampshire, Durham, NH 03824, USA
(3) Los Alamos National Laboratory, MS-D466, PO Box 1663, Los Alamos, NM 87545, USA
(4) Institute of Geophysics and extraterrestrial Physics, and Technical University of Braunschweig, Germany
|What triggers a substorm expansion phase onset?|
|Nishimura, Toshi, firstname.lastname@example.org (1)|
Sergeev, Victor, email@example.com (2)
|Starting a dialogue on this topic, which has been hot and controversial for more than 30 years (and continues to be so), we first briefly review a historical context of substorm triggering research and also step back and critically discuss a general approach --whether substorm onset definitions used in the community are adequate; --what are potential problems with the existing approach and other perspectives/choices/opportunities. Then we briefly summarize and discuss recent advances in substorm triggering research, attempting to address key questions of onset triggering (in observations, theory, modeling and mapping ): --Where in magnetosphere the auroral breakup/substorm onset are initiated?; --Which conditions are required to ignite the breakup/onset?; --Does onset require being triggered by precursors (flow burst intrusion etc.) or can be spontaneous?; --What is the mechanism of substorm onset (spontaneous or driven)? --What do control the size of processes after initial brightening?|
The dialogue also invites short presentations (1-2 slides with 1-2 brief statements) from the audience (please, inform us in advance) to form collectively a representative view where we are in this problem.
|(1) Department of Electrical and Computer Engineering and Center for Space Physics, Boston University, Boston, MA 02215, USA|
(2) Earth Physics Department, St. Petersburg State University, 198504 St. Petersburg, Russia
|Electric Current Systems associated with Poleward Boundary Intensifications (PBIs) of Auroral Emission|
|Ohtani, S., firstname.lastname@example.org (1)|
Motoba, T., email@example.com (1)
Gjeroloev, J. W., Jesper.Gjerloev@jhuapl.edu (1)
Ruohoniemi, J. M., firstname.lastname@example.org (2)
Donovan, E. F., email@example.com (3)
Yoshikawa, A., firstname.lastname@example.org (4)
|The present study is motivated by a recently proposed idea that the poleward boundary intensification (PBI) of auroral emission is an effect of electrostatic polarization. As the fast polar cap flow approaches the auroral oval, field-aligned currents (FACs) are induced at the poleward boundary because of the steep gradient of ionospheric conductance, which may be associated with the formation or intensification of an auroral form. In this study we examine four PBI events and address how well the observed longitudinal extension and associated current systems can be explained in terms of ionospheric polarization. The observations can be summarized as follows: (1) the PBIs actually take place equatorward of the open-closed boundary; (2) the PBIs are collocated with an upward FAC, which closes with an adjacent downward FAC through the ionosphere forming a longitudinally extending convection channel; (3) the PBIs extend longitudinally in the same direction as the longitudinal convection; (4) the PBIs extend both eastward and westward immediately following the arrival of the fast polar cap flow; (5) in one event ground magnetic variations can be explained by a moving upward FAC, which suggests that the current system associated with the PBIs is not unique. Whereas caution needs to be exercised in generalizing these results, they suggest that the ionospheric polarization plays an important role in the formation and evolution of the PBIs. It is also suggested that the spatial development of the PBIs may be preconditioned by preceding auroral activity and preexisting ionospheric convection.
|(1) The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA.|
(2) Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA.
(3) Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada.
(4) International Center for Space Weather Science and Education, Kyushu University, Fukuoka, Japan.
|Equatorial Magnetic Field of the Near-Earth Magnetotail: Search for a local minimum and tailward gradients|
|Ohtani, S., email@example.com (1)|
Motoba, T., firstname.lastname@example.org (1)
|The equatorial magnetic field of the nightside magnetosphere is critical for understanding not only the configuration of the magnetotail but also its state and dynamics. The present study observationally addresses various aspects of the equatorial magnetic field, such as its spatial distribution, possible antisunward gradients, and extremely weak magnetic fields, with an emphasis on the transition region between dipolar and stretched magnetotail configurations. The results are summarized as follows: (1) the equatorial magnetic field is better organized by the radial distance close to Earth but by the X distance farther down the tail, and at midnight this transition takes place statistically at X = -9 to -12 RE; (2) the average equatorial magnetic field in this transition region is noticeably weaker at solar minimum presumably reflecting weaker nightside magnetospheric currents closer to Earth; (3) the statistical comparison of equatorial magnetic fields measured simultaneously at two locations indicates that the gradient of the equatorial magnetic field is directed predominantly earthward, and it is suggested that apparent tailward gradients observed can be very often attributed to other factors such as structures in the Y direction and local fluctuations; (4) however, the gradient can be transiently directed tailward in association with the dipolarization of local magnetic field; (5) extremely weak (< 2 nT) magnetic fields are occasionally observed in the transition region during the substorm growth phase and during prolonged quiet intervals, but no clear association can be found with the steady driving of the magnetosphere possibly because of its rare occurrence.
|(1) The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA.|
|Current sheet thinning, reconnection onset, and auroral morphology during geomagnetic substorms|
|Otto, AO, email@example.com (1)|
Hsieh, MSH, firstname.lastname@example.org (1)
|Geomagnetic substorms represent a fundamental energy release mechanism for the terrestrial magnetosphere. Specifically, the evolution of thin currents sheets during the substorm growth phase plays a key role for substorms because such current sheets present a much lower threshold for the onset of tearing modes and magnetic reconnection than the usually thick magnetotail current sheet. Here we examine and compare two basic processes for current sheet thinning in the Earth's magnetotail: Current sheet thinning (1) through closed magnetic flux depletion (MFD) in the near Earth magnetotail caused by divergent flux transport to replace closed flux on the dayside and (2) through accumulation of open flux magnetic flux in the tail lobes also caused by dayside reconnection. Both processes are expected to operate during any period of enhanced dayside reconnection. It is demonstrated that closed magnetic flux depletion (MFD) in the near Earth magnetotail and the increase of open lobe magnetic flux can lead to the evolution of two separate thin current sheets in the near Earth and the mid tail regions of the magnetosphere. While the auroral morphology associated with MFD and near Earth current sheet formation is well consistent with typical substorm growth observation, midtail current sheet formation through lobe flux increase shows only a minor influence on the auroral ionosphere. We discuss the physics of the dual current sheet formation and local and auroral properties of magnetic reconnection in either current sheet. It is suggested that only reconnection onset in the near Earth current sheet may be consistent with substorm expansion because the flux tube entropy depletion of mid tail reconnection appears insufficient to cause geosynchronous particle injection and dipolarization. Therefore reconnection in the mid tail current sheet is more likely associated with bursty bulk flows or dipolarization fronts which stop short of geosynchronous distances.
|(1) Geophysical Institute, University of Alaska, Fairbanks, Alaska|
|Plasma sheet currents associated with oscillatory flow braking|
|Panov, E.V., email@example.com (1)|
Nakamura, R., firstname.lastname@example.org (1)
Baumjohann, W., email@example.com (1)
Weygand, J.M. firstname.lastname@example.org (2)
Russell, C.T., email@example.com (2)
Giles, B.L., firstname.lastname@example.org (3)
|Braking of earthward reconnection outflows at ~10 Re down the Earth's magnetotail can produce oscillations in the magnetic field and currents. Oscillatory flow braking (OFB) involves side vorticity, ionospheric energy losses through aurora, and may modulate particle injection into the inner magnetosphere. Hence, it is important to study the regions of transient enhanced currents that are born in the plasma sheet during OFB. Here we use an MMS OFB event on 9 August 2016 to identify and study the transient enhanced current regions in the plasma sheet boundary layer.
|(1) Space Research Institute, Austrian Academy of Sciences, Graz, Austria|
(2) Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA
(3) NASA Goddard Space Flight Center, Greenbelt, MD, USA
|Spatial correspondence between Pi2 wave power and UV aurora bursts|
|Pilipenko, V.A., email@example.com (1)|
Martines-Bedenko, V.A., firstname.lastname@example.org (2)
Engebretson, M.J., email@example.com (3)
Moldwin, M.B., firstname.lastname@example.org (4)
|We have examined snapshots of overlaid ultra-violet auroral images from POLAR and IMAGE spacecraft and ULF wave power in the Pi2 frequency band. The latitudinal distribution of Pi2 spectral power, as well as the position of the ionospheric electrojet, are inferred from the MACCS-CARISMA-MEASURE array of magnetic stations. A substorm develops as a series of "detonations", accompanied by an enhancement of auroral luminosity, intensification of the ionospheric currents, and a burst of Pi2 wave power. The epicenter of each detonation leaps during each activation poleward and westward. The latitudinal location of the auroral ionospheric electrojet and Pi2 power is found to be mainly associated with the poleward border of the auroral activation region. The result of case studies is supported by statistical superposed epoch latitudinal distributions of the auroral intensity and Pi2 power. This result may help to identify a possible channel of Pi2 wave energy transmission from the magnetotail to the ground.
|(1) Space Research Institute, Moscow|
(2) Institute of the Physics of the Earth, Moscow
(3) Augsburg University, Minneapolis, MN
(4) University of Michigan, Ann Arbor, MI
|Excitation and Structuring of Auroral Arcs in Ionospheric Regions of Low Conductance |
|Prakash, M., email@example.com (1,2)|
|Current studies attempt to address the formation of latitudinally narrow auroral arcs and their relationship with larger-scale global magnetospheric processes. These studies use the nonlinear dispersive field line resonance (NDFLR) model where the structures of auroral arcs are sustained by field line resonances (FLRs). The model describes the competition between ionospheric feedback, nonlinear, and dispersive effects in a curvilinear geomagnetic topology. It also accounts for nonlinear modulation of the ionospheric conductance. The Pedersen conductance is modulated by hundreds of eV electrons that precipitate in the ionosphere through the action of shear Alfvén wave field-aligned currents (FACs). The interplay between the ionospheric feedback dissipation, wave dispersion, and nonlinearity results in large-amplitude, long-period oscillations of the FACs, in emission of slow-moving small-scale secondary auroral arcs, and density perturbations. Using observed values of night side conductivities and realistic topology of geomagnetic field lines, FLRs with frequencies in the range of a few mHz, spatial scales up to several kilometers near the ionosphere, and FAC amplitudes extending to tens of mA/m2 are obtained. The NDFLR model explains the excitation of structured auroral arcs in regions of low ionospheric conductance. The results are reviewed in the context of available auroral imaging data on magnetosphere-ionosphere coupling.|
Nonlinear Effects in Geomagnetic Field Resonances, J. Geophys. Res., 108 (A4), 8014, 2003
|(1) Department of Physics and Astronomy, Hofstra University, Hempstead, New York 11549|
(2)Department of Physics, Farmingdale State College, New York 11735
|Effects of storms and substorms in the Southern Ionosphere during solar cycle 23|
|Prince, P.R., firstname.lastname@example.org (1)|
Seema, C.S., email@example.com (1)
|Solar events such as coronal mass ejection and solar flares intensify solar wind and carry large amount of energetic particles towards the magnetopause. Coupling of the earth's magnetosphere and the intensified solar wind disturbs the geomagnetic field and generates field aligned currents, enhancing the ionospheric currents below and within the auroral oval. This in turn produces geomagnetic storms and substorms that leads to complex ionospheric dynamics, and variations, which play a serious role in radio wave propagation, satellite tracking, navigation, etc. Geomagnetic storms and substorms ,measured quantitatively by the geomagnetic indices such as Dst, AE, AL ,AU etc., cause the ionospheric peak electron density (Nmax) to increase/decrease from their quiet-time levels, resulting in positive/negative ionospheric storms. The F2 layer critical frequency (foF2) is an important parameter for understanding the dynamics of the F2 region, since it is directly related to the Nmax of ionospheric plasma. The production, loss, and transport of ions which shape the ionospheric dynamics, depend mainly on the variation of solar zenith angle, neutral composition, neutral temperature and neutral winds. Variability of ionospheric parameters with distinct periodicities of 11 years, 1 year, 6 months , 24 hours, etc. mainly owe to geomagnetic and meteorological activities or abrupt changes caused principally by geomagnetic storms and substorms. In the present study, the time lag of foF2 variability due to storms and substorms, in five stations in the southern hemisphere, during solar cycle 23 has been addressed. The stations fall in different latitudes and in more or less same longitudes so that the local time for the stations falls within a difference of only one hour. A time lagged linear regression analysis of 0-72 hours over a whole solar cycle was done between percentage deviation of foF2 from quiet time value and geomagnetic indices to investigate the overall ionosphere.
|(1) Department of Physics, University College, Trivandrum, India, 695034|
|Kinetic Effects in Magnetotail Dynamics: Emergence of Finite-Width Reconnection Exhausts and the Occurrence of Localized Reconnection Onset |
|Pritchett, P.L., firstname.lastname@example.org (1)|
|3-D particle-in-cell simulations are used to investigate two aspects of magnetic reconnection in a magnetotail configuration: (1) the emergence of finite-width exhaust structures from a X line and (2) the localized onset of reconnection in response to the imposition of a near-Earth, high-latitude electric field. Both issues are addressed using an initial plasma sheet configuration that consists of a 2-D dipole field joined to an asymptotic tail equilibrium with finite Bz. |
An earthward-moving reconnection jet from a finite X line is found to separate initially into two segments of width ~10-15 di each. The dawnward segment moves ahead of the duskward one due to a finite ion-gyroradius effect and continues to intensity, while the latter is buffeted by the return flows generated by the former and stagnates. The leading front develops the characteristic structure of a sharp Bz increase and density drop on a 1-2 di scale. The current associated with this Bz increase is carried mainly by the electrons, and the jet front is the site of a Region 1 sense field-aligned current system. Close to the dipole region the ion velocity distribution behind the front contains a drop out in parallel phase space at speeds of ~1.5-2.5 VA.
It has been difficult to understand the emergence of localized (in y) reconnection flow channels in the tail. Unlike the case of a localized driving Ey applied in the lobes, which spreads rapidly across the tail due to the high Alfven speed, a localized Ey imposed at high latitude on the earthward boundary remains localized and creates a Bz reduction region that stretches duskward. This leads to a dawn-dusk asymmetry with a thinner current sheet and weakened Bz on the duskward edge of the flow channel. Eventually, this leads to localized reconnection with a tilted X line and the emergence of strong earthward and tailward flows. The significance for substorm onset will be discussed.
|(1) Department of Physics & Astronomy, UCLA, Los Angeles, CA 90095-1547, USA|
|Non-extensive analysis of magnetospheric substorm dynamics|
|Prince, P.R., email@example.com (1)|
Sumesh Gopinath, firstname.lastname@example.org (1)
|The existence of characteristic signatures related with dynamical phase transitions which arise during the period of substorms have always been a subject of interest in magnetospheric substorm research. Substorms are characteristic phenomena in which sudden unloading of energy marks the onset of magnificent auroral displays seen in the polar-high latitude regions. Here the stored magnetic energy is spontaneously converted to plasma kinetic energy, resulting in dramatic changes both in the large-scale topology of the night-side geomagnetic field as well as in the energetic particle flux in near-Earth space. Nonlinear measures have been proven effectively applicable for the study of dynamical phase transitions related with self-organization, cooperative behavior, non-extensiveness in magnetosphere during substorms. During past few years, empirical evidence has been mounting in support of the possibility that a number of complex systems arising in diverse disciplines may have certain quantitative features that are surprisingly similar. Such features of similarity can be conveniently classified under the paradigm of 'universality'. In other words, the dynamics of complex systems are founded on universal principles that can be used to describe disparate problems. The non-extensive Tsallis statistical mechanics provides a firm basis for analyzing out-of-equilibrium complex systems that may exhibit long-range correlations, memory, or fractal properties and hence considered as an appropriate mathematical tool to investigate 'universality'. We analyze the scope of employing novel non-extensive techniques for analyzing the magnitude distribution of substorms in order to investigate the existence of a universal behavior as well as to compute the relations of degree of non-extensiveness in complex magnetospheric substorm dynamics.
|(1) Department of Physics, University College, Trivandrum-695034, Kerala, India|
|Some characteristics and associated nightside ionospheric joule heating studies of substorms on St. Patrick's Day 2015 geomagnetic storm|
|Prince, P.R., email@example.com (1)|
Suji, K.J., firstname.lastname@example.org (1)
|The first super storm of solar cycle 24 occurred on "St. Patricks's day" (17 March 2015), with a minimum Dst level of -223 nT. Some striking characteristics of substorms and subsequent variations in joule heating, over night side auroral ionosphere, during the super storm are presented in this study. 6 major substorms were selected, with its minimum values of local electrojet index (IL) ranging from -1662 nT to -673 nT. The selected substorms are all in midnight sector showing negative bay in x component of magnetogram, derived from the IMAGE magnetometer longitudinal (fennoscandia) chain. The solar wind energy input is estimated as time integral of Akasofu's epsilon parameter, determined from SuperMAG magnetometer. The northern hemisphere joule heating rates are estimated using Ahn's empirical conversion and its time integral from onset phase to recovery phase gives the Joule heat energy, which ranges from from 1.2 ×1015J to 5.9×1015J, for the selected events. A close correlation is obtained between the solar wind energy input parameter and the Joule heat energy. This high correlation is a characteristic of directly driven (DD) processes and the selected substorms are proved to be falling in the DD category. In addition, the ionospheric joule energy over midnight sector also shows good correlation with the solar wind energy, which again validates the presence of DD scenario.
|(1) Department of Physics, University College, Trivandrum, India, 695034|
|Probing Near-Earth Reconnection Ejecta in the Near Tail and at Lunar Orbit|
|Runov, A. email@example.com (1)|
|Near-Earth magnetotail reconnection is the vital element of a substorm. Transient localized dipolarizations and associated electric field pulses, known as dipolarizing flux bundles (DFBs) and rapid flux transfers (RFTs) are remote signatures of near-Earth reconnection. Statistical studies of DFBs/RFTs observed in the plasma sheet at geocentric distances 7 to 25 Earth's radii (RE) and at lunar orbit (~60 RE) in the tail revealed that they are localized in the earth-tail (X) and cross-tail (Y) directions and their equatorial cross-section dimensions are of 1 to 5 RE (tens of ion inertial lengths). These localized area of the enhanced north-south magnetic field component and cross-tail electric field field (reconnection ejecta) are dominantly observed in the pre-midnight magnetotail. We present results of a comparative statistical analysis of earthward and tailward reconnection ejecta properties, such as magnetic and electric fields, particle distributions and their moments, observed in near-Earth tail and at lunar orbit by THEMIS and ARTEMIS probes, respectively.
|(1) University of California Los Angeles|
|Simulation Study of Small-scale Plasma / Neutral Dynamics from Electron Precipitation|
|Sadler, F.B., firstname.lastname@example.org (1)|
Lessard, M., email@example.com (1)
Otto, A., firstname.lastname@example.org (2)
|Soft electron precipitation is known to initiate a range of ionospheric and thermospheric reactions, such as increased temperature, density, and upwelling. Due to the complex coupling of these reactions with the underlying plasma and neutral populations, a straightforward interpretation of the underlying physics is problematic. We investigate the small-scale dynamics associated with electron precipitation using a kilometer-scale, three-fluid, ionosphere-thermosphere numerical model which includes inertial ion and neutral terms. Simulation results are presented which detail the temporal evolution of plasma and neutral populations over a range of electron precipitation energy & energy flux inputs. The timescales of the responses vary from a few seconds (electrons) to 10s of seconds (ion upwelling) to 10s of minutes (plasma density and neutral upwelling). When viewed at these small time-scales upward moving wave-like reactions emerge which increase in amplitude with increasing altitude.
|(1) University of New Hampshire, Durham, NH 03824|
(2) Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775-7320
|A Statistical Analysis of Pi1B Seasonal Variations and Generating Mechanisms|
|Salzano, M.L., email@example.com (1)|
Lessard, M.R., firstname.lastname@example.org (1)
Kim, H., email@example.com (2)
Engebretson, M.J., firstname.lastname@example.org (3)
Posch, J.L., email@example.com (3)
|Pi1B magnetic pulsations are characterized by irregular ULF broadband bursts, with periods of between 1-40 seconds, and are well correlated with substorm onsets. There has been debate over the years regarding the source of these pulsations. Heacock  originally suggested that Pi1B pulsations result from small-scale, local ionospheric currents at substorm onset. Arnoldy et al.  discovered that these pulsations are observed at geosynchronous orbit at onset, implying that they originate beyond geosynchronous orbit and not in the ionosphere. Motivated by papers showing interhemispheric differences in substorm evolution [Papitashvili et al., 2002], as well as the Newell et al.  result, where the authors used satellite data in a comprehensive statistical study to conclude that intense aurora occur only when the background ionospheric conductivity is low (i.e., it is not sunlit), a preliminary study of Pi B pulsation arrival times has been carried out, comparing onset times at the South Pole and Iqaluit, its approximate magnetic conjugate in northern Canada. During the spring of 1995, ground signatures of Pi1B pulsations at the South Pole tended to lead those at Iqaluit often by a minute or two, with a wide distribution in time differences. During the fall of 1995, however, events at Iqaluit tended to lead those at the South Pole, but with significantly smaller time differences and with less scatter than in the spring. This preliminary study suggests the presence of a seasonal dependence in Pi1B onset times in opposite hemispheres. Further work will analyze a much larger data set for purposes of improved statistical significance.
|(1) Space Science Center, University of New Hampshire, Durham, NH., USA.|
(2) Center for Solar-Terrestrial Research, New Jersey Institute of Technology, Newark, NJ., USA.
(3) Physics Dept., Augsburg College, Minneapolis, MN., USA
|Study of the July 12, 2012 Coronal Mass Ejection and its impact at Earth with EUHFORIA: a heliospheric-magnetospheric model chain approach|
|Scolini, C., firstname.lastname@example.org (1,2)|
Poedts, S., email@example.com (1)
Chané, E., firstname.lastname@example.org (1)
|Coronal Mass Ejections (CMEs) and their interplanetary counterparts are considered to be the major space weather drivers, and an accurate modelling of their onset and propagation up to 1 AU represents a key issue for more reliable space weather forecasts. However, accurate evaluations of the geomagnetic activity triggered by an impacting CME can only be performed by coupling heliospheric models to 3D models describing the terrestrial environment, e.g. magnetospheric and ionospheric codes in the first place.|
In this work we test the predictive capabilities of the newly developed EUHFORIA heliospheric model both in terms of the solar wind predictions at L1, and in terms of the induced geomagnetic activity predicted at ground level. In order to achieve this goal, we make use of a coupled model chain approach by using EUHFORIA outputs at Earth as input parameters for the OpenGGCM and GUMICS magnetospheric models.
In particular, we present an analysis of the July 12, 2010 CME, observed by the SOHO and STEREO missions in coronagraphic and interplanetary images, that caused a moderate geomagnetic storm recorded on ground.
We first simulate the event with the EUHFORIA+Cone model, using CME input parameters determined by multi-spacecraft reconstruction techniques. We then study the propagation and global evolution of the CME up to its arrival at Earth, where we compare in-situ measurements of the Interplanetary CME, with the parameters derived from simulations. We use EUHFORIA outputs at L1 as boundary conditions for the OpenGGCM and GUMICS magnetospheric models, so to study the induced perturbation on the system and the expected on-ground geomagnetic activity level in terms of the Kp and Dst indices. We compare these predictions with on-ground actual data records and with results obtained by the use of empirical relations linking solar wind parameters at L1 to global geomagnetic activity indices. Finally, we discuss the forecasting capabilities of such kind of approach and its future improvements.
|(1) Centre for mathematical Plasma Astrophysics (CmPA), KU Leuven, 3001 Leuven, Belgium|
(2) Solar-Terrestrial Centre of Excellence, SIDC, Royal Observatory of Belgium, 1180 Brussels, Belgium
|Does local B-minimum appear in the tail current sheet during substorm growth phase?|
|Sergeev, V., email@example.com (1)|
Gordeev, E., firstname.lastname@example.org (1)
Merkin, V., Slava.Merkin@jhuapl.edu (2)
Sitnov M., Mikhail.Sitnov@jhuapl.edu (2)
|Possibility of midtail magnetic configurations with non-monotonous radial variation of BZ-component in the tail current sheet has been discussed recently in relation to the substorm onset triggering problem, because the regions of tailward dBZ/dr are known to be potentially unstable to a number of instabilities. Observational answer to this question is hard to get from existing sparse fleet of magnetospheric spacecraft. Remote sensing from low-altitude spacecraft offers more possibilities, by providing a profile of energetic particles precipitating from different distances in the tail current sheet, whose loss-cone filling rate depends on magnetic field curvature and, therefore, carries information about the radial distribution of equatorial B in the plasma sheet. Particularly, for energetic electrons (Ee> 30..100 keV) the dipolarized portions of midtail current sheet (where BZ>5..10nT) are expected to be seen as regions of anisotropic (empty loss cone) electrons embedded in the regions of isotropic loss cone precipitation, associated with stretched (small BZ and/or large current density) current sheet region. |
Here we report the observations of six POES spacecraft during intense solar electron event with a good coverage of substorm growth phase, during which we systematically detected signatures of localized dipolarized region embedded into the stretched current sheet region, located about 1deg CGLatitude poleward of outer boundary of the radiation belt, that is somewhere in the midtail. We briefly discuss the threshold nature of this method as well as the characteristics of BZ peak which can produce observed behavior of energetic particle flux.
|(1) Department of Earth's Physics, St Petersburg State University, St-Petersburg, Russia|
(2) Applied Physics Laboratory, John Hopkins University, Laurel, MD, USA
|Ten Years in Orbit: THEMIS and the Earth's Magnetosphere|
|Sibeck, D.G., email@example.com (1)|
|The THEMIS mission, comprising 5 identical equatorial spacecraft and an extensive array of ground based all-sky imagers and magnetometers, marked its tenth anniversary in February 2017. Over the past decade, researchers both within and outside the original team have made numerous discoveries related to the dayside solar wind-magnetosphere interaction, the Earth's radiation belts, and substorms. Kinetic processes operating in the foreshock and magnetosheath generate a host of structures, some of which batter the magnetosphere, trigger magnetic reconnection on the dayside magnetopause, and initiate geomagnetic pulsations. The magnetosheath was surveyed and the Kelvin-Helmholtz instability was found to be far more prevalent than once suspected. Surveys of the occurrence patterns for chorus, hiss, magnetosonic, and EMIC waves capable of interacting with radiation belt electrons and poloidal pulsations capable of interacting with ring current ions provided the information needed to understand the origins of these waves and evaluate their importance to radiation belt physics. Two of the spacecraft were detached from the near-Earth formation and sent to the Moon at the ARTEMIS mission. Researchers employing ARTEMIS observations have made numerous discoveries concerning the interaction of the solar wind with the Moon, its exosphere, and the formation of the lunar wake. However, as promised in the original proposal, THEMIS has made its greatest contributions to our understanding of processes that occur within the Earth's magnetotail. The mission has answered longstanding questions concerning the origin of discrete, diffuse, and pulsating aurora. With regards to geomagnetic substorms, the 5 original and 3 remaining THEMIS spacecraft have demonstrated that many substorms begin with the onset of reconnection in the mid-magnetotail, that launch dipolarization fronts followed by bursty bulk flows that propagate Earthward, generate field-aligned currents, and launch particle injections into the ring current. THEMIS ground- and space-based observations have prompted the development of new models in which streamers launched by dayside reconnection propagate across the polar cap to trigger substorms when they reach the nightside auroral oval. THEMIS welcomes joint studies with other missions and takes pro-active measures to ensure that NASA's Heliophysics Division accomplishes systems science objectives.
|(1) Code 674, NASA/GSFC, Greenbelt, MD 20771, USA|
|Spontaneous reconnection in the magnetotail: Multiscale kinetic picture|
|Sitnov, M. I., Mikhail.Sitnov@jhuapl.edu (1)|
Merkin, V. G., Slava.Merkin@jhuapl.edu (1)
Garcia-Sage, K., firstname.lastname@example.org (2)
|At least some substorms are likely caused by a reconnection instability in the tail current sheet. A fundamental problem in theory and modeling of such spontaneous reconnection is that the tearing instabilities in the tail are almost fully prohibited. Due to the stabilizing effect of electrons magnetized by the magnetic field Bz normal to the current plane, the tearing stability region extends from global to micro (electron gyroradius) scales. Moreover, the tearing instability starting at macro scales is only possible for special classes of magnetotail equilibria possessing a tailward Bz gradient. However, such equilibria are also prone to non-reconnection ballooning/interchange and flapping instabilities of the current sheet, which may dominate reconnection in driving the system toward the topology change locally in the dawn-dusk direction or destroy the reconnection-prone equilibrium with a tailward Bz gradient before reconnection starts. Nevertheless, global MHD simulations show that potentially tearing-instable configurations with tailward Bz gradients do naturally appear as a result of the solar wind loading (southward IMF Bz) at about 20 Re downtail. They stay there for tens of minutes occupying a broad (several hours) area in local time The kinetic behavior of such tail configurations is governed by the competition between tearing and non-reconnection instabilities depends on the current sheet thickness and on the background (lobe) plasma population. We present results of 3D PIC simulations with open boundaries in large simulation boxes to show that the tearing instability dominates non-reconnection plasma motions even in the absence of a background and with current sheets thicker than the thermal ion gyroradius. We also discuss specific observational signatures of both the initial unstable configuration and the subsequent spontaneous reconnection process, including the Hall magnetic field patterns, plasma dissipation, plasma anisotropy and agyrotropy.
|(1) Johns Hopkins University Applied Physics Laboratory, 11101 Johns Hopkins Rd., Laurel MD 20723-6099|
(2) NASA Goddard Space Flight Center, Greenbelt, MD 20771
|Alfvenic generation of Substorm Auroras and Triggers of Substorm Onset|
|Song, Yan, email@example.com (1)|
Lysak, L.R., firstname.lastname@example.org (1)
|Substorms result from the dynamical response of the M-I coupling system to external solar wind driving and to internal dynamics. Substorms have been often referred to as auroral substorms. The substorm onset and its expansion and recovery phases have mainly been described by the morphology of auroral arcs during substorms (Akasofu, 1964). In this presentation, we emphasize that understanding the physics of the generation of substorm auroral arcs is the key to understanding the triggering mechanism of substorm onset.|
It is well known that a necessary condition for the occurrence of substorms is the accumulation of free energy stored in the magnetotail during the growth phase. We have suggested that another necessary condition for producing substorm expansion phase is to have a large earthward force acting in the magnetotail (Lin et al., 2009; Song and Lysak, 2012). During the growth phase, energy and momentum are transferred from the solar wind into the magnetosphere. At this stage, the M-I coupling system, which is constantly driven by the solar wind, is far from a thermal equilibrium. Thus, a decrease in momentum transfer from the solar wind into the magnetosphere due to, for example, an IMF northward turning, will start a preconditioning stage, and cause force imbalance, producing a net earthward body force acting on the magnetotail. This earthward force can cause a large scale movement of the tail towards a more dipole-like configuration.
During the preconditioning stage, the generation of parallel electric fields and the formation of substorm auroral arcs in localized regions at the equatorward boundary can redistribute perpendicular mechanical and magnetic stresses in auroral flux tubes, decoupling the magnetosphere from ionosphere drag locally. This will enhance the tail earthward shear flows and rapidly buildup stronger parallel electric fields in the auroral acceleration region, leading to a sudden and violent tail energy release.
Parallel electrostatic electric fields are effective in accelerating auroral particles to high energy, creating auroral arcs. In particular, Alfvenic double layers, produced by non-linear interaction of incident and reflected Alfven wave packets in the M-I coupling system, can act as a powerful high energy particle accelerator. The Poynting flux carried by Alfven waves can continuously supply a large amount energy from the generator region in the magnetotail to the auroral acceleration region, producing substorm auroral arcs. During the expansion phase, the formation of enhanced substorm auroral arcs is powerful means to rapidly convert the accumulated free magnetic energy stored in the magnetotail to the kinetic energy of charged particles that produce substorm auroral arcs.
|(1) School of Physics and Astronomy, University of Minnesota, 116 Church Street, S.E., Minneapolis, MN 55455, USA|
|Combined Global MHD and Test-Particle Simulation of a Radiation Belt Storm: Comparing Depletion, Recovery and Enhancement with in Situ Measurements|
|Sorathia, K., Kareem.Sorathia@jhuapl.edu (1)|
Ukhorskiy, A.Y., email@example.com (1)
Lyon,J., firstname.lastname@example.org (2)
|During geomagnetic storms the intensities of radiation belt electrons exhibit dramatic variability. In the main phase electron intensities exhibit deep depletion over a broad region of the outer belt. The intensities then increase during the recovery phase, often to levels that significantly exceed their pre-storm values. In this study we analyze the depletion, recovery and enhancement of radiation belt intensities during the 2013 St. Patrick's geomagnetic storm. We simulate the dynamics of high-energy electrons using our newly-developed test-particle radiation belt model (CHIMP) based on a hybrid guiding-center/Lorentz integrator and electromagnetic fields derived from high-resolution global MHD (LFM) simulations. Our approach differs from previous work in that we use MHD flow information to identify and seed test-particles into regions of strong convection in the magnetotail. We address two science questions: 1) what are the relative roles of magnetopause losses, transport-driven atmospheric precipitation, and adiabatic cooling in the radiation belt depletion during the storm main phase? and 2) to what extent can enhanced convection/mesoscale injections account for the radiation belt buildup during the recovery phase? Our analysis is based on long-term model simulation and the comparison of our model results with electron intensity measurements from the MAGEIS experiment of the Van Allen Probes mission.
|(1) Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723|
(2) Dartmouth College, Hanover, NH 03755
|The Nonlinear Dynamics of Substorms with the WINDMI Model|
|Spencer, E.A., email@example.com (1)|
Srinivas, P.K., firstname.lastname@example.org (1)
Vadepu, S.K., email@example.com (1)
Crabtree, C., firstname.lastname@example.org (2)
Horton, W., email@example.com (3)
|We discuss a low order physics model of the nightside magnetosphere called WINDMI. The model uses solar wind and IMF measurements from the ACE spacecraft as input into a system of 8 nonlinear ordinary differential equations. The state variables of the differential equations represent the energy stored in the geomagnetic tail, central plasma sheet, ring current and field aligned currents. The output from the model is the geomagnetic westward auroral electrojet (AL) index, and the Dst index. We will show how the model has been used to analyze the dynamics of substorms.|
Three classes of magnetospheric substorms are studied with the model, isolated substorms, storm time substorms, and periodic substorms. We analyze the model predictions to obtain the statistical average of the energy content in the earth's ring current, central plasma sheet and magnetotail prior to substorm onset. We use these statistical averages and their time rate of change to evaluate the possibility of several different instability mechanisms being the driver of substorm onset.
|(1) Electrical and Computer Engineering Dept., Univ. of South Alabama|
(2) US Naval Research Laboratory
(3) Dept. of Geophysics, Applied Research Laboratories, The University of Texas at Austin, TX, USA
|Global empirical model of substorms derived from spaceborne magnetometer data|
|Stephens, G.K., firstname.lastname@example.org (1)|
Sitnov, M.I., email@example.com (1)
Korth, H., firstname.lastname@example.org (1)
Gkioulidou, M., email@example.com (1)
Ukhorskiy, A.Y., firstname.lastname@example.org (1)
|Characteristic changes in the global geomagnetic field and underlying picture of electric currents during magnetospheric substorms are described using an advanced version of the empirical geomagnetic field model TS07D. The new model uses two regular expansions of the equatorial currents with distinctly different scales, corresponding to thick and thin current sheets relative to the thermal ion gyroradius, and arbitrary distribution of those currents in the equatorial plane, constrained only by data. Such a multi-scale description allows one to reproduce the current sheet thinning in the growth phase. The model also uses a flexible description of field-aligned currents reproducing their spiral structure at low altitudes and providing a continuous transition from region 1 to region 2 current systems. The empirical picture of substorms is obtained by combining magnetometer data from ACE, Wind, Geotail, THEMIS, Van Allen Probes, Cluster II, Polar, IMP-8, GOES 8, 9, 10 and 12 and then binning this data based on similar values of the auroral index AL, its time derivative and the integral of the solar wind electric field parameter in time over substorm scales. The events considered include substorms on 26 February 2008 and 3 July 2012, which had multi-probe coverage and were extensively debated in the community, as well as the collection of substorms during the March 2008 storm. It is shown that the AL binning helps reproduce dipolarization signatures in the northward magnetic field Bz, while the solar wind electric field integral allows one to capture the current sheet thinning in the growth phase. The model allows one to trace the substorm dipolarization from the tail to the inner magnetosphere where the dipolarization of strongly stretched tail field lines causes a redistribution of the tail current ending by an enhancement of the partial ring current in the premidnight sector.
|(1) The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA|
|Magnetospheric Multiscale Observations of Field-Aligned Currents in the Magnetotail|
|Strangeway, R.J., |
Anderson, B. J.,
Weygand, J. M.,
Kepko, E. L.,
Slavin, J. A.,
Paterson, W. R.,
Giles, B. L.,
Shuster, J. R.,
Torbert, R. B.,
Burch, J. L.
|Field-aligned currents (FACs) are frequently observed by MMS at the dayside magnetopause, which are of the order 100s of nA/m^2, the magnetotail FACs are relatively weak, of the order 10s of nA/m^2. There appear to be a variety of sources for the FACs. FACs are observed in association with dipolarization fronts that are propagating both earthward and tailward, at the boundary of the current sheet, and in flux-ropes. FACs are also observed to be embedded in regions of high speed flow, both earthward and tailward, and not just at the dipolarization front frequently associated with high speed flows. As is the case for FACs observed at the dayside magnetopause, these observations raise questions as to how or where the FACs close.
|MESSENGER observations of tail dynamics during substorm at Mercury|
|Sun, W.J., email@example.com (1, 2)|
Slavin, J.A., firstname.lastname@example.org (3)
Fu, S.Y., email@example.com (2)
Raines, J.M., firstname.lastname@example.org (3)
Poh, G.K., email@example.com (3)
Pu, Z.Y., firstname.lastname@example.org (2)
Zong, Q.G., email@example.com (2)
Wei, Y., firstname.lastname@example.org (1)
Wan, W.X., email@example.com (1)
|MESSENGER magnetic field and plasma measurements taken in Mercury's magnetotail have been examined for substorm activity. A number of tail passes were found to contain clear Earth-like growth and expansion phase features. During the growth phase, we have observed plasma sheet thinning and lobe field increases. We have also observed dipolarizations, plasma waves (e.g., Pi2-like pulsations), and plasma sheet thickening during the expansion phase. These features were similar to what is observed at Earth. However, the time scale of Mercury substorms is only several minutes (~ 2 - 3 mins) comparing with the several hours (~ 2 - 3 hrs) at Earth [Slavin et al., 2010; Sun et al., 2015a, 2015b]. Detailed analysis of protons during substorm dipolarizations have revealed energization and heating. Statistical study has further revealed that proton supra-thermal particle flux and proton temperature distributions in near-Mercury central plasma sheets display dawn-dusk asymmetries, with higher values in the dawnside plasma sheet than in the duskside. We propose that these dawn-dusk asymmetries could be due to the fact that more substorm dipolarizations were initiated on the dawnside, i.e., postmidnight, of Mercury's magnetotail [Sun et al., 2017]. These distributions are consistent with features of magnetic reconnection in the near-Mercury-neutral-line region [Sun et al., 2016], but are opposite from those observed at Earth, where magnetic reconnection occurred more often in the duskside plasma sheet and ion and electron dispersionless injections were more frequently observed in the pre-midnight plasma sheet.|
Slavin, J. A., et al. (2010). MESSENGER observations of extreme loading and unloading of Mercury's magnetic tail. Science, 329, 665-668. doi:10.1126/science.1188067.
Sun, W.-J., J. A. Slavin, S. Y. Fu, et al. (2015a), MESSENGER observations of magnetospheric substorm activity in Mercury's near magnetotail. Geophys. Res. Lett., 42, 3692-3699. doi: 10.1002/2015GL064052.
Sun, W.-J., J. A. Slavin, S. Y. Fu, et al. (2015b), MESSENGER observations of Alfvénic and compressional waves during Mercury's substorms. Geophys. Res. Lett., 42, 6189-6198. doi: 10.1002/ 2015GL065452.
Sun, W. J., et al. (2016), Spatial distribution of Mercury's flux ropes and reconnection fronts: MESSENGER observations, J. Geophys. Res.: Space Physics, 121(8), 7590-7607.
Sun, W. J., et al. (2017), MESSENGER observations on the energization and heating of protons in the near Mercury magnetotail, submitted to Geophys. Res. Lett..
|(1) Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China.|
(2) School of Earth and Space Sciences, Peking University, Beijing, China.
(3) Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA.
|Entropy in the plasmasheet/inner magnetospheric physics|
|Toffoletto, F., firstname.lastname@example.org (1)|
Yang,.J., email@example.com (1)
Wolf, R. A., firstname.lastname@example.org (1)
Sazykin, S., email@example.com (1)
|The flux tube entropy, defined as S=∫(p^(1/γ) ds/B), where p is the pressure and B is the magnetic field strength and the integral path (s) is over an entire flux tube, is conserved along a flow streamline in ideal MHD. On average, S increases tailward, so that the nightside tail region tends to be stable against interchange. In order for a plasma-sheet flux tube to be transported into the inner magnetosphere from the plasmasheet, its S value must be reduced so that it reaches equilibrium in a region where it matches the background value closer to the Earth. The most obvious way to reduce S is through magnetic reconnection in the tail, which is believed to be sporadic and results in transient bursts of rapid transport, termed "bursty bulk flows (BBFS) " or "bubbles". In this presentation, we will describe the impact of these low S bubbles on the inner magnetosphere and their role in substorms and ring current injection. For example, our simulations show that the main contribution to ring current energy during an intense storm main phase comes from particles inside bubble channels, and that during a substorm expansion such channels can contribute to the formation of the substorm current wedge.
|(1) Physics and Astronomy Department, MS 108, Rice University, Houston, TX|
|MMS Pursuit of Electron Diffusion Regions in the Earth's Magnetotail|
|Torbert,R.B 1,2, |
and the Entire MMS Team
|The Magnetospheric Multiscale (MMS) fleet of four spacecraft has now completed Phase 2B, the magnetotail phase, of its prime mission. The objective of this phase is to study symmetric reconnection at electron scales as they may occur during events in the range of 15-25 Re down the magnetotail. The MMS team has found and greater than 30 electron diffusion events of asymmetric character at the dayside magnetopause. EDRs in the nightside magnetotail were expected to be and, in fact have been, much more elusive. This talk will discuss some dayside events and describe our search to date for nightside events
|1University of New Hampshire;|
2Southwest Research Institute
|New insights on energetic particle injections and substorm activity from Magnetospheric Multiscale (MMS) and Van Allen Probes|
|Turner, D. L. (1) |
Fennell, J. F. (1)
Blake, J. B. (1)
Claudepierre, S. G. (1)
Clemmons, J. H. (1)
Jaynes, A. N. (2)
Leonard, T. (2)
Baker, D. N. (2)
Cohen, I. J. (3)
Gkioulidou, M. (3)
Ukhorskiy, A. Y. (3)
Mauk, B. H. (3)
Gabrielse, C. (4)
Angelopoulos, V. (4)
Strangeway, R. J. (4)
Kletzing, C. A. (5)
Le Contel, O. (6)
Spence, H. E. (7)
Torbert, R. B. (7,8)
Burch, J. L. (8)
Reeves, G. D. (9)
|This presentations examines multipoint observations of energetic particle injections and associated substorm activity using NASA's Magnetospheric Multiscale (MMS) and Van Allen Probes missions. In particular, we focus on multipoint observations during a conjunction between MMS and Van Allen Probes on 07 April 2016 in which a series of energetic particle injections occurred. With complementary data from THEMIS, Geotail, and LANL-GEO (16 spacecraft in total), we develop new insights on the nature of energetic particle injections associated with substorm activity. Despite this case involving only weak substorm activity (max. AE < 300 nT) during quiet geomagnetic conditions in steady, below-average solar wind, a complex series of at least six different electron injections was observed throughout the system. Intriguingly, only one corresponding ion injection was observed. All ion and electron injections were observed at < 600 keV only. MMS reveals detailed substructure within the largest electron injection. A relationship between injected electrons with energy < 60 keV and enhanced whistler-mode chorus wave activity is also established from Van Allen Probes and MMS. Drift mapping using a simplified magnetic field model provides estimates of the dispersionless injection boundary locations as a function of universal time, magnetic local time, and L-shell. The analysis reveals that at least five electron-only injections, which were localized in magnetic local time, preceded a larger injection of both electrons and ions across nearly the entire nightside of the magnetosphere near geosynchronous orbit. The larger, ion and electron injection did not penetrate to L < 6.6, but several of the smaller, electron-only injections penetrated to L < 6.6. Due to the discrepancy between the number, penetration depth, and complexity of electron vs. ion injections, this event presents challenges to the current conceptual models of energetic particle injections.
|(1) The Aerospace Corporation, El Segundo, CA, USA|
(2) LASP, University of Colorado, Boulder, CO, USA
(3) Applied Physics Laboratory, Johns Hopkins University, Laurel, MD, USA
(4) University of California, Los Angeles, CA, USA
(5) University of Iowa, Iowa City, IA, USA
(6) CNRS/Ecole polytechnique/UPMC Univ. Paris 06/Univ. Paris-Sud/Observatoire de Paris, Paris, France
(7) University of New Hampshire, Durham, NH, USA
(8) Southwest Research Institute, San Antonio, TX, USA
(9) Los Alamos National Laboratory, Los Alamos, NM, USA
|Proton Transport and Acceleration at Dipolarization Fronts: High-Resolution MHD/Test-Particle Simulations|
|Ukhorskiy, A.Y., firstname.lastname@example.org (1)|
Sorathia, K., Kareem.Sorathia@jhuapl.edu (1)
Mitchell,D.G., Don.Mitchell@jhuapl.edu (1)
Wiltberger, M., email@example.com (2)
Lyon,J., firstname.lastname@example.org (3)
|Much of plasma heating and transport from the magnetotail into the inner magnetosphere occurs in the form of mesoscale discrete injections associated with sharp dipolarizations of magnetic field (dipolarization fronts). In this study we investigate the mechanisms of ion acceleration at dipolarization fronts in a high-resolution global magnetospheric MHD model (LFM). We use large-scale three-dimensional test-particle simulations (CHIMP) to address the following science questions: 1) what are the characteristic scales of dipolarization regions that can stably trap ions? 2) what role does the trapping play in ion transport and acceleration? 3) how does it depend on particle energy and distance from Earth? 4) to what extent ion acceleration is adiabatic? High-resolution LFM was run using idealized solar wind conditions with fixed nominal values of density and velocity and a southward IMF component of -5 nT. To simulate ion interaction with dipolarization fronts, a large ensemble of test particles distributed in energy, pitch-angle, and gyrophase was initialized inside one of the LFM dipolarization channels in the magnetotail. Full Lorentz ion trajectories were then computed over the course of the front inward propagation from the distance of 17 to 6 Earth radii. A large fraction of ions with different initial energies stayed in phase with the front over the entire distance. The effect of magnetic trapping at different energies was elucidated with a correlation of the ion guiding center and the ExB drift velocities. The role of trapping in ion energization was quantified by comparing the partial pressure of ions that exhibit trapping to the pressure of all trapped ions.
|(1) Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723|
(2) NCAR, Boulder, CO 80305
(3) Dartmouth College, Hanover, NH 03755
|Two-fluid MHD simulations on ballooning instability of Earth's magnetotail|
|Wang, Z.-C., email@example.com (1)|
Zhu, P., firstname.lastname@example.org (1,2)
|Previous single-MHD simulations demonstrate that the ballooning instability in Earth's magnetotail grows and evolves in certain thin-current sheet configurations, which would in turn induce plasmoid formation and magnetic reconnection in the magnetotail [1,2]. How the two-fluid effects may affect the onset of ballooning instability as well as the subsequent plasmoid formation process in magnetotail as predicted in the single-MHD simulations, remains an open question. In this work, we address such a question using the two-fluid MHD model in NIMROD code. Both linear and nonlinear calculations are carried out to evaluate the two-fluid effects on the ballooning instability and its consequence, based on a generalized Harris sheet configuration of the magnetotail. The progress and status of the work will be reported and discussed.|
 P. Zhu and J. Raeder, Phys. Rev. Lett. 110, 235005 (2013).
 P. Zhu and J. Raeder, J. Geophys. Res. Space Physics 119, 131-141 (2014).
|(1) University of Science and Technology of China, Hefei, Anhui 230026, China|
(2) University of Wisconsin-Madison, Madison, WI 53706, USA
|Alfvenic turbulence in auroral magnetosphere-ionosphere coupling|
|Watanabe, T.-H., email@example.com (1)|
Kaneyama, M., firstname.lastname@example.org (1)
Maeyama, S., email@example.com (1)
|The feedback instability is known to be destabilized in the magnetosphere-ionosphere (M-I) coupling, when the magnetospheric convection velocity exceeds a critical value. During the instability growth, the shear Alfven waves are amplified with enhancement of the field aligned current and the ionospheric density perturbations. Development of the local field-aligned current circuit is associated with spontaneous excitation of auroral arc structures and electron precipitation.|
The feedback instability has widely been investigated both in the linear and the weak nonlinear regimes while the full nonlinear study is limited so far. Nonlinear saturation of the feedback instability growth is discussed in terms of the secondary instability [1,2], where the Kelvin-Helmholtz type mode is generated by a sheared ExB flow. Recently, we have developed a new nonlinear simulation code for the M-I coupling, and applied it to investigate a long-time evolution of the feedback instability.
In the fully nonlinear stage of the feedback instability, we have found transition to turbulence through the M-I coupling , where the energy equipartition is observed in the Alfvenic turbulence. During the tradition phase, auroral vortices are also observed in terms of the ionospheric density enhancement and depletion. The obtained results provide a novel theoretical understanding on spontaneous generation of Alfvenic turbulence observed in auroral regions.
 T.-H. Watanabe, Phys. Plasmas 17, 022904 (2010).
 T.-H. Watanabe, H. Kurata, and S. Maeyama, New J. Phys. 18, 125010 (2016).
|(1) Department of Physics, Nagoya University, Nagoya 464-8602, Japan|
|Ballooning and feedback instabilities in the magnetosphere-ionosphere coupling|
|Watanabe, T.-H., firstname.lastname@example.org (1)|
|In this study, we consider competition of two types of instabilities in the magnetosphere-ionosphere (M-I) coupling, that is, the ballooning and the feedback instabilities.|
The ballooning instability has been investigated as a possible mechanism for triggering the substorm in the magnetosphere. It is known to be destabilized, when the pressure gradient coupled with the magnetic curvature overcomes the stabilization effect due to the field line bending. Simultaneously, in the M-I coupling system in polar regions, the shear Alfven waves (or the kinetic Alfven waves) can also be destabilized through the magnetospheric convection, if the ionospheric density change is taken into account with the feedback mechanism [1-3]. As the field line bending is related to the shear Alfven wave propagation, the above situation is regarded as a competition of the two types of instabilities with different energy sources.
We have investigated the ballooning and the feedback instabilities in the same theoretical model of the M-I coupling. Our linear analysis demonstrates that, as the interchange term enhances, the "unstable" shear Alfven waves with the opposite sign of the real eigenvalues in their lowest harmonic branch collide with each other and transit to the ballooning mode. When the magnetospheric convection is weak, however, the feedback instability can not grow while the ballooning mode remain to be excited by the pressure gradient.
The present theory implies that competition of the two instabilities may give a plausible explanation of auroral beading triggered through the M-I coupling.
 T. Sato, J. Geophys. Res., 83, doi:10.1029/JA083iA03p01042.
 T.-H. Watanabe, Phys. Plasmas, 17, 022904 (2010).
 T.-H. Watanabe, Geophys. Res. Lett., 41, doi:10.1002/2014GL061166 (2014).
|(1) Department of Physics, Nagoya University, Nagoya 464-8602, Japan|
|Temporal and Spatial Development of dB/dt During Substorms|
|Weygand, J.M., email@example.com (1)|
Gabrielse, C., firstname.lastname@example.org (1)
|Ground induced currents (GICs) due to space weather are a threat to high voltage power transmission systems. However, knowledge of ground conductivity is the largest source of error in the determination of GICs. A good proxy for GICs is dB/dt determined from the Bx and By component of the magnetic field fluctuations. Using two dimensional maps of dB/dt over North America and Greenland derived from the spherical elementary currents we investigate the temporal and spatial change of dB/dt for both a single event and a two dimensional superposed epoch analysis. Both the single event and the statistical analysis show a sudden increase of dB/dt at substorm onset followed by an expansion poleward, westward, and eastward of the onset during the expansion phase. The temporal and spatial development resembles the temporal and spatial change of the auroral emissions. During all of the expansion phase dB/dt values exceed the maximum thresholds outlined in Pulkkinen et al. [2011; 2013] over significant areas. In the recovery phase the dB/dt values gradually decrease and recover about 25 min after the auroral onset.
|(1) Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East Box 951567, Los Angeles, CA 90095-1567|
|What is most urgently needed to make progress in substorm physics: A tail constellation,imagers, or better models?|
|Wiltberger, M., email@example.com|
Kepko, E. L., firstname.lastname@example.org
|In this debate the authors will discuss which of two approaches will most rapidly advance substorm physics. On one side, the focus will be on the deployment of constellation of spacecraft in the magnetotail. On the other side the focus will be on the a focus on the the development of improved models of geospace.
|(1) NCAR/NASA, Boulder CO |
(2) NASA/GSFC, Greenbelt, MD
|Quasi-Separatrix Layers Induced by Ballooning Instability in Earth's Magnetotail|
|Zhu, P., email@example.com (1,2)|
Wang, Z.-C., firstname.lastname@example.org (1)
|Previous MHD simulations have revealed the dynamically three-dimensional (3D) nature of the magnetic reconnection process induced by ballooning instability in Earth's magnetotail [1,2]. Represented by a generalized Harris sheet, the magnetotail configuration itself is two dimensional due to the symmetry in the dusk-dawn direction. Under certain conditions, such a configuration can become unstable to ballooning instabilities, which in its nonlinear stage can induce the formation of plasmoids, even though there is no pre-existing X-line in the near-Earth magnetotail region. Based on those simulation results, the spatial distribution and structure of the quasi-separatrix layers induced by ballooning instability in Earth's Magnetotail, as well as their temporal evolution, are examined in this work, which indicate that the associated magnetic reconnection can only occur in 3D geometry and is thus irreducible to that of any two-dimensional reconnection process . Such a finding may provide a new perspective to the long-standing controversy over the substorm onset problem, in particular on the potential roles of reconnection and ballooning instabilities. It may also connect to the universal presence of 3D reconnection processes previously discovered in various natural and laboratory plasmas.|
 P. Zhu and J. Raeder, Phys. Rev. Lett. 110, 235005
 P. Zhu and J. Raeder, J. Geophys. Res. Space Physics
119, 131-141 (2014).
 P. Zhu, A. Bhattacharjee, A. Sangari, Z.-C. Wang, and
P. Bonofiglo, Phys. Plasmas 24, 024503 (2017).
|(1) University of Science and Technology of China, Hefei, Anhui 230026, China|
(2) University of Wisconsin-Madison, Madison, WI 53706, USA
|Dynamics of the Sub-Auroral Polarization Streams during geomagnetic disturbances and their relations with energetic particle injection|
|Zihan, Z.W., email@example.com (1)|
Shasha, S.Z., firstname.lastname@example.org (1)
|Sub-Auroral Polarization Streams (SAPS) refer to regions with intense radial electric fields in the inner magnetosphere and poleward electric fields in the conjugate subauroral ionosphere. These large electric fields lead to westward convection flows and sometimes decrease the electron density in the ionosphere. SAPS are important in the magnetosphere-ionosphere-thermosphere coupling process. However, their evolution during geomagnetic disturbances, especially their relationship with energetic particle injections are still not well understood. In this study, we report a conjugate observation of SAPS from the Van Allen Probes (VAP) and the Defense Meteorological Satellite Program (DMSP) on May 18, 2013. In this case, VAP observed large SAPS electric field (~10mV/m) pointing radially outward at the plasmapause. At the same time, a dispersionless energetic particle injection was also observed. However, the magnetic field variations were not consistent with those associated with standard dipolarization fronts. Instead, two pairs of bipolar magnetic field perturbations in the X, Y and Z direction in GSE coordinate near the plasmapause were observed. This signature could be generated by two pairs of field-aligned currents (FACs) with large amplitude. We discuss possible physical connections between the energetic particle injection, the formation of SAPS and field-aligned currents.
|(1) Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, 2455 Hayward St. |
|Dynamic Evolution of Polar Cap Patches During Substorms|
|Zou, S., email@example.com (1)|
Wang, Z., firstname.lastname@example.org (1)
Ren, J., email@example.com (1)
Ozturk, D., firstname.lastname@example.org (1)
|Polar cap patches refer to the islands of high F-region and topside plasma density within the polar cap. Their dynamic evolution from the dayside to the nightside is not very well understood. The F-region ionosphere density is strongly influenced by convection electric field, thermospheric wind as well as soft particle precipitation. This study combines observations from multiple instruments, including Poker Flat incoherent scatter radar (PFISR), GPS total electron content (TEC) and optical instruments, as well as the Global Ionosphere and Thermosphere Model (GITM), to investigate the effects of highly structured electric fields, such as those associated with auroral streamers and subauroral polarization streams (SAPS), and thermospheric winds on the dynamic evolution of polar cap patches during substorms. We also discuss variation of the optical emission associated with the patch evolution and its contribution to the substorm growth phase redline emission.
|(1) Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, USA.|