Sarah Vines | Searcharxiv

arXiv2025

Field Aligned Currents and Auroral Precipitation During the Terrestrial Alfven Wing State

When sub-Alfv\'enic (Alfv\'en Mach number MA < 1) plasmas impact Earth, Alfv\'en wings (AWs) develop. A Multiscale Atmosphere Geospace Environment (MAGE) simulation of the April 2023 storm, validated by Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) data, reveals the field-aligned-current (FAC) generation mechanism and predicts auroral precipitation for Earth's AWs. Simulation and observations show northern hemisphere planetward flowing electrons are predominantly at magnetic local times (MLTs) 8-13. Before the AWs formed, solar wind conditions were similar and MA ~ 1.4, yet the same FAC system extended from 9-18 MLT. Flow vorticity drives FACs at the boundary of the AWs and unshocked solar wind. The AW shape presents a different obstacle to the solar wind compared to typical lobe fluxes, producing the unique FAC distribution. New insights about AW FACs and precipitating electron energy flux will help understand auroral features for exoplanets inside their host star's Alfv\'en zone.

physics.space-ph↗

arXiv2020

Magnetohydrodynamic with embedded particle-in-cell simulation of the Geospace Environment Modeling dayside kinetic processes challenge event

We use the MHD with embedded particle-in-cell model (MHD-EPIC) to study the Geospace Environment Modeling (GEM) dayside kinetic processes challenge event at 01:50-03:00 UT on 2015-11-18, when the magnetosphere was driven by a steady southward IMF. In the MHD-EPIC simulation, the dayside magnetopause is covered by a PIC code so that the dayside reconnection is properly handled. We compare the magnetic fields and the plasma profiles of the magnetopause crossing with the MMS3 spacecraft observations. Most variables match the observations well in the magnetosphere, in the magnetosheath, and also during the current sheet crossing. The MHD-EPIC simulation produces flux ropes, and we demonstrate that some magnetic field and plasma features observed by the MMS3 spacecraft can be reproduced by a flux rope crossing event. We use an algorithm to automatically identify the reconnection sites from the simulation results. It turns out that there are usually multiple X-lines at the magnetopause. By tracing the locations of the X-lines, we find the typical moving speed of the X-line endpoints is about 70~km/s, which is higher than but still comparable with the ground-based observations.

physics.space-ph↗