Localized and intense energy conversion in the diffusion region of asymmetric magnetic reconnection

TL;DR

This paper investigates localized energy dissipation during asymmetric magnetic reconnection at the magnetopause, revealing the dominant role of Hall magnetic field annihilation and electron dynamics, supported by high-resolution simulations and MMS observations.

Contribution

It uncovers the mechanism of intense localized dissipation in asymmetric reconnection, emphasizing the importance of Hall magnetic field annihilation over symmetric reconnection processes.

Findings

Localized dissipation exceeds expectations by over an order of magnitude.

Hall magnetic field annihilation is the primary driver of energy conversion.

Electron jets and field-aligned beams match MMS observations.

Abstract

We analyze a high-resolution simulation of magnetopause reconnection observed by the Magnetospheric Multiscale (MMS) mission and explain the occurrence of strongly localized dissipation with an amplitude more than an order of magnitude larger than expected. Unlike symmetric reconnection, wherein reconnection of the ambient reversed magnetic field drives the dissipation, we find the annihilation of the self-generated, out-of-plane (Hall) magnetic field plays the dominant role. Electrons flow along the magnetosheath separatrices, converge in the diffusion region, and jet past the X-point into the magnetosphere. The resulting accumulation of negative charge generates intense parallel electric fields that eject electrons along the magnetospheric separatrices and produce field-aligned beams. Many of these features match MMS observations.