Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm33a2124l&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM33A-2124
Physics
[2736] Magnetospheric Physics / Magnetosphere/Ionosphere Interactions, [2764] Magnetospheric Physics / Plasma Sheet
Scientific paper
We show the relation between precipitating electrons at auroral altitudes and their magnetospheric source region through three geomagnetic conjunction events during magnetically quiet conditions (AE < 50nT). We have investigated electron spectra simultaneously observed by the FAST satellite at altitudes of 2500-3500km and by the THEMIS satellite in the plasma sheet at 7-13Re. Time resolutions of the FAST and THEMIS electron measurements are 1-3sec and 1-7min, respectively. To consider ambiguity of field-line mapping, we investigate the FAST data ±30sec from the preliminary conjugate time. We compare the spectral shapes and energy fluxes of electrons at two different altitudes. As for the event-1 at 19:15:00±30sec UT on 10 April 2008, the electron energy flux obtained by FAST is significantly lower than that of THEMIS at the estimated conjugate time (19:15:20 UT based on the T89 model). However, at 19:14:30 UT, which is 50sec before the estimated conjugate time, the electron spectrum in perpendicular pitch angle at FAST is well correlated with the spectrum in parallel pitch angle at THEMIS for an energy range of 0.3-4keV. Higher energy electrons above 5keV are continuously missing at FAST for all the time range at 19:14:30-19:15:30 UT. For the event-2 at 12:55:00±30sec UT on 26 April 2008, the electron spectral shape in perpendicular pitch angle at FAST is well consistent with that of parallel pitch angle at THEMIS at estimated conjugate time at 12:55:10 UT. For the event-3 at 00:58:00±30s UT on 25 December 2008, uniformly precipitating high-energy electrons above 300eV and low-energy inverted-V shaped electrons below 300eV with monoenergetic peaks at 100-200eV are simultaneously observed at FAST. The spectral shape of the high-energy electrons in perpendicular pitch angle at FAST is very well correlated with that of parallel pitch angle at THEMIS, while the low-energy electrons with monoenergetic peak at FAST are not seen in the THEMIS electron spectrum. From these results, we suggest that the non-accelerated precipitating electrons at auroral altitudes directly come from the equatorial plasma sheet, except for the high-energy part of event 1. In this presentation, we will discuss the possible mechanisms for missing of the high-energy electrons of event-1 and the source region of the low-energy electrons with monoenergetic peak measured by FAST for event-3.
Lee Seongsu
McFadden James P.
Shiokawa Kazuhiko
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