Journal Article

A THEMIS multicase study of dipolarization fronts in the magnetotail plasma sheet

Li, S., Angelopoulos, V., Zhang, X.-J., Runov, A., Zhou, X.-Z., Plaschke, F., Bonnell, J.

2011

Overview

We discuss results of a superposed epoch analysis of dipolarization fronts, rapid (δt < 30 s), high‐amplitude (δBz > 10 nT) increases in the northward magnetic field component, observed during six Time History of Events and Macroscale Interactions during Substorms (THEMIS) conjunction events. All six fronts propagated earthward; time delays at multiple probes were used to determine their propagation velocity. We define typical magnetic and electric field and plasma parameter variations during dipolarization front crossings and estimate their characteristic gradient scales. The study reveals (1) a rapid 50% decrease in plasma density and ion pressure, (2) a factor of 2–3 increase in high‐energy (30–200 keV) electron flux and electron temperature, and (3) transient enhancements of ∼5 mV/m in duskward and earthward electric field components. Gradient scales of magnetic field, plasma density, and particle flux were found to be comparable to the ion thermal gyroradius. Current densities associated with the Bz increase are, on average, 20 nA/m2, 5–7 times larger than the current density in the cross‐tail current sheet. Because j · E > 0, the dipolarization fronts are kinetic‐scale dissipative regions with Joule heating rates of 10% of the total bursty bulk flow energy. Key Points Superposed epoch analysis of THEMIS dipolarization front events Common pattern in field and particle variations during front crossings Particle energization and energetic plasma transport

• Publisher: Blackwell Publishing Ltd
• Subject: Atmospheric sciences / Electric fields / Magnetic fields / Magnetism / magnetotail / Plasma physics / plasma sheet / reconnection / Space