ICS-13 Abstract View


Stormtime Substorms: Occurrence Features and Flow Channel Triggering
Lyons, L.R., larry@atmos.ucla.edu (1)
Zou, Y., yingzou@bu.edu(2)
Nishimura, Y., toshi@atmos.ucla.edu(1.2)
Gallardo-Lacourt, B.. beatriz.gallardo@ucalgary.ca (3)
E. F. Donovan, E.F., edonovan@ucalgary.ca (3)
Angelopoulos, V., vassilis@igpp.ucla.edu (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.