A statistical study on the whistler waves behind dipolarization fronts

Abstract

AbstractWe present a statistical study of whistler waves behind dipolarization fronts (DFs) based on the Cluster satellites measurements during the years 2001–2007. We find 732 DFs during the 7 year tail periods (XGSM ≤ −8 RE and |YGSM| ≤ 10 RE) in the plasma sheet. By constraining the whistler waves in a 1 min interval behind the DFs (the maximum Bz), we find that 381 DFs (about 50%) are followed by whistler waves. We study the occurrence rate of whistler waves, the wave characteristic parameters, and the corresponding electron distribution, not only in a global view but also in the local DF coordinate. In a global view, behind the DFs, the whistler waves mostly occur in the radial distance between 17 and 18 RE. They have a higher occurrence rate on the dawnside than the duskside. On the other hand, in the local DF coordinate, whistler waves have a higher occurrence rate around the meridian of DF. In addition, the average wave amplitudes increase toward the dawnside of DF. Associated with the whistler waves, electron distributions have a dominant perpendicular anisotropy for electrons with energy higher than 5 keV. Lower energy electron distributions do not have such perpendicular anisotropy dominance. Moreover, the perpendicular anisotropy for electrons >5 keV increases toward the dawnside of DF, which may be caused by the drift‐betatron acceleration. We suggest that the free energy source for whistler waves behind the DFs is probably the perpendicular anisotropy of >5 keV electrons caused by the betatron acceleration.