Electron Pitch Angle Distributions in Compressional Pc5 Waves by THEMIS-A Observations

Abstract

Although compressional Pc5 waves are well known in the energy conversion and regulation of charged particles in the magnetosphere, the detailed features of associated electron pitch angle distributions (ePADs) are poorly understood. Based on Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations from 2010 to 2016, ePADs in the magnetic decreases (troughs) of compressional Pc5 waves are classified into three types: cigar, butterfly, and pancake. They are found in the electrons with respective energy ranges of 100–1,000 eV (larger than 10 keV), 1–10 keV (larger than 1 keV), and 6–30 keV (100 eV–10 keV) in (non)whistler-type compressional Pc5 waves, that is, cases where whistler-mode waves are present (absent) in the magnetic troughs. These statistical ePAD features observed in the whistler- and nonwhistler-type waves are suggested to be associated with the Landau resonance of whistler-mode waves and drift-shell splitting effect.