Characterizing Ion Flows Across a Dipolarization Jet

TL;DR

This study uses particle-in-cell simulations to analyze how the structure of dipolarization jets in Earth's magnetotail depends on their dawn-dusk width, revealing effects on magnetic and ion flow structures.

Contribution

It provides new insights into how jet width influences magnetic field configurations and ion flow speeds in dipolarization jets, including the reversal of Hall magnetic fields.

Findings

Magnetic field and ion flow structures depend on jet width.

Reversal of Hall magnetic field observed in larger jets.

Ion flow speed approaches Alfvén speed when jet width exceeds ion Larmor radius.

Abstract

The structure of dipolarization jets with finite width in the dawn-dusk direction relevant to magnetic reconnection in the Earth's magnetotail is explored with particle-in-cell simulations. We carry out Riemann simulations of the evolution of the jet in the dawn-dusk, north-south plane to investigate the dependence of the jet structure on the jet width in the dawn-dusk direction. We find that the magnetic field and Earth-directed ion flow structure depend on the dawn-dusk width. A reversal in the usual Hall magnetic field near the center of the current sheet on the dusk side of larger jets is observed. For small widths, the maximum velocity of the Earthward flow is significantly reduced below the theoretical limit of the upstream Alfv\'en speed. However, the ion flow speed approaches this limit once the width exceeds the ion Larmor radius based on the normal magnetic field, $B_z$.