ICS-13 Abstract View


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, k-nishi@isee.nagoya-u.ac.jp (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