Statistical Study of Electron Kinetic Entropy Generation at Earth's Quasi-perpendicular Bow Shock

Abstract

We use the Magnetospheric Multiscale mission to study electron kinetic entropy across Earth's quasi-perpendicular bow shock. We perform a statistical study of how the change in electron entropy depends on the different plasma parameters associated with a collisionless shock crossing. We find that the change in electron entropy exhibits strong correlations with upstream electron plasma beta, Alfvén Mach number, and electron thermal Mach number. The source of entropy generation is investigated by correlating the change in electron entropy across the shock to the measured electric and magnetic field wave power strengths for different frequency intervals within different regions in the shock transition layer. The electron entropy change is observed to be greater for higher electric field wave power within the shock ramp and shock foot for frequencies between the lower hybrid frequency and electron cyclotron frequency. This implies electrostatic waves are important for electron kinetic entropy generation at Earth's quasi-perpendicular bow shock but also for the non-adiabatic electron heating at quasi-perpendicular shocks.