Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm53b..07b&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM53B-07
Physics
[2716] Magnetospheric Physics / Energetic Particles: Precipitating, [2720] Magnetospheric Physics / Energetic Particles: Trapped, [2778] Magnetospheric Physics / Ring Current, [2788] Magnetospheric Physics / Magnetic Storms And Substorms
Scientific paper
We report on the dynamics of low-altitude energetic neutral atom (ENA) emissions during two substorms that occurred during the main phases of two storms: (1) a CME-driven storm on 5 April 2010 and (2) a CIR-driven storm on 11 October 2008. For both of these storms, we employ observations from multiple complementary observing platforms. The dual-spacecraft Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission obtained ENA images containing low altitude emissions (LAEs). Substorm dynamics is inferred from THEMIS all-sky imagers. TWINS-observed LAEs are compared with precipitating/trapped proton fluxes from NOAA/MetOp constellation. We find that the timing and intensity profiles of LAEs are different for the two selected events, and account for the different LAE behavior as resulting from different pitch-angle distributions of the two source ion populations. For the 11 October 2008 event, the LAEs seem closely coupled with the ring current ENA emissions, and seem roughly correlated with the SYMH index. From NOAA/MetOp data, the trapped and precipitating fluxes during this event are approximately the same. On 5 April 2010, NOAA/MetOp data show the formation of a trapped ring current with an empty loss cone during the substorm recovery phase; LAEs are decoupled from ring current emissions and follow roughly the auroral activity. We conclude that strong precipitation may account for unusually low SYMH variation for this event in comparison with auroral indices. We also note that the LAE response for our two selected events differs from the results of a statistical study of proton substorm aurora. We conclude that LAEs are produced not directly by precipitating particles (proton aurora), but probably by trapped particles near loss cone, consistent with the predictions of thick target approximation (TTA) theory.
Buzulukova N.
Fok M. H.
Goldstein Jeffrey Jay
McComas David John
Redfern J. A.
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