Electromagnetic waves and electron anisotropies downstream of supercritical interplanetary shocks

TL;DR

This study analyzes electromagnetic wave observations downstream of supercritical interplanetary shocks, revealing that whistler waves are driven by heat flux instability and influence electron heat flux and temperature anisotropy.

Contribution

It provides new observational evidence linking whistler waves to heat flux regulation and electron anisotropy near interplanetary shocks.

Findings

Whistler waves correlate with heat flux and electron temperature anisotropy.

Lower hybrid waves are associated with magnetic field gradients.

Mixed wave events suggest combined wave influences.

Abstract

We present waveform observations of electromagnetic lower hybrid and whistler waves with f_ci << f < f_ce downstream of four supercritical interplanetary (IP) shocks using the Wind search coil magnetometer. The whistler waves were observed to have a weak positive correlation between \partialB and normalized heat flux magnitude and an inverse correlation with T_eh/T_ec. All were observed simultaneous with electron distributions satisfying the whistler heat flux instability threshold and most with T_{perp,h}/T_{para,h} > 1.01. Thus, the whistler mode waves appear to be driven by a heat flux instability and cause perpendicular heating of the halo electrons. The lower hybrid waves show a much weaker correlation between \partialB and normalized heat flux magnitude and are often observed near magnetic field gradients. A third type of event shows fluctuations consistent with a mixture of both lower hybrid and whistler mode waves. These results suggest that whistler waves may indeed be regulating the electron heat flux and the halo temperature anisotropy, which is important for theories and simulations of electron distribution evolution from the sun to the earth.