Double layers in the Earth's bow shock

TL;DR

This paper reports observations of electrostatic double layers in Earth's bow shock, revealing their characteristics, potential drops, and role in electron heating, which enhances understanding of shock physics.

Contribution

It provides the first detailed measurements of electrostatic double layers in Earth's bow shock, highlighting their properties and impact on electron temperature.

Findings

Double layers have electric fields up to 100 mV/m.

Potential drops are 2-7% of the cross-shock potential.

Electron temperature increases across double layers.

Abstract

We present Magnetospheric Multiscale observations of electrostatic double layers in quasi-perpendicular Earth's bow shock. These double layers have predominantly parallel electric field with amplitudes up to 100 mV/m, spatial widths of 50-700 m, and plasma frame speeds within 100 km/s. The potential drop across a single double layer is 2-7% of the cross-shock potential in the de Hoffmann-Teller frame and occurs over the spatial scale of ten Debye lengths or one tenth of electron inertial length. Some double layers can have spatial width of 70 Debye lengths and potential drop up to 30% of the cross-shock potential. The electron temperature variation observed across double layers is roughly consistent with their potential drop. While electron heating in the Earth's bow shock occurs predominantly due to the quasi-static electric field in the de Hoffmann-Teller frame, these observations show that electron temperature can also increase across Debye-scale electrostatic structures.