Geomagnetic conjugate observations of plasma-sheet electrons by the FAST and THEMIS satellites

Abstract

We investigate pitch-angle distributions and spectral shapes of auroral electrons simultaneously observed during three conjunction events by the FAST satellite at altitudes of 2500-3500 km and by the THEMIS satellite in the plasma sheet at 7-13 RE. All three events were on the lower latitude of the auroral oval. Conjunction event 1 occurred at ~1914:45 UT on 10 April 2008. Electron spectra at energies of 0.1-3 keV are correlated well between the two satellites, while the precipitating electrons above 3 keV are missing at FAST. Event 2 occurred at 1255:26 UT on 26 April 2008. Electron spectra above 3 keV are correlated well between the two satellites. An additional broad spectral peak at energies of 0.1-0.5 keV was observed by FAST. Event 3 occurred at 0058:04 UT on 25 December 2008. Precipitating electrons of 0.5-5 keV obtained by FAST are correlated well with those of THEMIS-C, while a monoenergetic peak at 0.1-0.2 keV was observed only by FAST. For the three conjunction events, we conclude that high-energy precipitating auroral electrons observed by FAST directly come from the equatorial plasma sheet, while low-energy precipitating electrons may come from middle altitudes as a result of acceleration by static potential differences. For missing high-energy (>3 keV) electrons of event 1, we speculate that the pitch-angle scattering by waves occurs only at a limited energy range. ©2012. American Geophysical Union. All Rights Reserved.