Publication Date:
2013-11-09
Description:
[1] During the interval ~07:45:36–07:54:24UT on 24 August 2005, Cluster satellites (C1 and C3) observed an obvious loss of energetic electrons (~3.2-95 keV) associated with the growth of whistler mode waves inside some bursty bulk flows (BBFs) in the midtail plasma sheet ( X GSM ~ −17.25R E ). However, the fluxes of the higher-energy electrons (≥128 keV) and energetic ions (10-160 keV) were relatively stable in the BBF-impacted regions. The energy-dependent electron loss inside the BBFs is mainly due to the energy-selective pitch angle scatterings by the whistler mode waves within the scattering time scales from several seconds to several minutes, and the pitch angle evolutions of the resonant electrons in different initial distributions are different in the wave growth regions. The low-energy plasma sheet electrons (~0.073-2.1 keV) have initially a field-aligned pitch angle distribution (0 o ≤ α ≤ 30 o and 150 o ≤ α ≤ 180 o ) in the absence of the whistler mode waves, and the loss of the low-energy electrons in field-aligned directions is accompanied by their increase in quasi-perpendicular directions (30 o 〈 α 〈 150 o ) in the intense wave growth regions inside the BBFs, indicating that the resonant electrons in a field-aligned pitch angle distribution can be scattered by the waves simultaneously into the loss cone and towards the larger pitch-angles. Due to the limits of the small loss cone ( α c ~ 0.8-1.3 o ) and double-direction scatterings in field-aligned distributions, the loss of the low-energy electrons inside the BBFs is not obvious in the presence of their large background fluxes. Unlike the low-energy electrons, the plasma sheet energetic electrons (~3.2-95 keV) have mainly a quasi-perpendicular pitch angle distribution (30 o 〈 α 〈 150 o ) during the expansion-to-recovery development of a substorm ( AE index decreased from 1677nT to 1271nT), and their loss can occur at almost all pitch angles in the intense wave growth regions inside the BBFs, indicating that the resonant electrons in a quasi-perpendicular pitch angle distribution are always scattered by the waves from the larger pitch angles to the loss cone. Finally, the growth of whistler mode waves causes the net loss of the quasi-perpendicular distribution electrons inside the BBFs. These observations indicate that the anisotropic distribution energetic electrons mainly undergo the rapid pitch angle scattering loss because of the growth of whistler mode waves inside the BBFs with a highly compressed equatorial magnetic field (~tens of nT), but the final loss effect of the wave-induced pitch angle scatterings on resonant electrons depends on their initial pitch angle distributions.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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