On the role of system size in Hall MHD magnetic reconnection

TL;DR

This paper investigates how system size influences magnetic reconnection in Hall MHD, revealing different reconnection regimes, flux-pileup effects, and the impact of grid scale on reconnection dynamics.

Contribution

It provides new insights into the dependence of reconnection regimes on system size and grid scale in Hall MHD simulations of magnetic island coalescence.

Findings

Large system sizes exhibit both Sweet-Parker-like and Petschek-like reconnection regimes.

Flux-pileup effects cause islands to bounce despite fast reconnection.

Peak reconnection rates approach 0.1 vA B0, but average rates remain slow.

Abstract

We study the effects of the Hall electric field on magnetic island coalescence in the large island limit and find evidence for both a elongated electron current sheet layer with a Sweet-Parker-like reconnection rate and a collapsed, Petschek-like electron sheet with a peak reconnection rate approaching the 0.1 vA B0 Hall MHD rate. The state observed in our simulations appears to depend on grid scale. Furthermore, even at the largest system sizes, we find that flux-pileup effects cause the islands to "bounce" despite the presence of a collapsed current sheet allowing for fast instantaneous reconnection. The average reconnection rate in the large island limit is slow though the peak reconnection rate is fast.