Wave and particle characteristics of earthward electron injections associated with dipolarization fronts

Abstract

A comprehensive examination of particle and wave data from multiple Thermal Emission Imaging System (THEMIS) satellites has been made of an electron injection structure in the magnetotail as it propagated earthward from −20 R E to −11 R E on 27 February 2009. The electron injection, which was closely associated with a dipolarization front and bursty bulk flows, occurred within a thin plasma boundary layer and had both perpendicular and parallel energization, with very little energy dispersion. The thin plasma boundary layer had a thickness comparable to the ion inertial length and displayed different plasma characteristics at different locations. Strong electromagnetic waves between the lower hybrid frequency and the electron gyrofrequency, as well as electrostatic waves up to the electron plasma frequency, were observed within the thin plasma boundary layers. The two outermost spacecraft at X = −20.1 R E and X = −16.7 R E detected intense whistler waves, most likely driven by an observed electron temperature anisotropy with T ⊥ / T ∥ > 1. Closer to Earth at X = −11.1 R E , whistlers were not seen, consistent with the observed electron distribution having T ⊥ / T ∥ < 1. Near the electron injection region, nonlinear electrostatic structures such as electrostatic solitary waves and double layers were also observed. These nonlinear electrostatic structures can interact with the electron distribution and accelerate electrons; high energy distributions could be generated if the electrons encountered a large number of these structures. The observations show that nonideal MHD, nonlinear, and kinetic behavior is intrinsic to the electron injections with multiscale coupling.