Multispecies MHD Simulations of the Crustal Field Influence at the Mars Magnetotail Current Sheet

Abstract

The magnetotail current sheet of Mars exhibits a dawn-to-dusk asymmetry that has been seen in satellite observations and MHD simulations. However, the influence of season has not been thoroughly investigated in MHD simulations. This investigation incorporates seasonal variations, driven by planetary eccentricity and solar variability, within the BATS-R-US multispecies MHD code to examine the influence of crustal magnetic fields and the ionosphere on the magnetotail current sheet. The solar wind interaction at Mars is analyzed for the following cases: solar maximum at perihelion (PERMAX), solar maximum at aphelion (APHMAX), solar minimum at perihelion (PERMIN), and solar minimum at aphelion (APHMIN). Simulation results show that the current sheet exhibits a duskward shift at solar maximum and a dawnward shift at solar minimum. In simulations that omit the crustal sources, the current sheet remains symmetric along the $Y=0$ plane. Because these results did not induce a shift, the ionization rates were adjusted for the PERMAX and APHMIN cases. The ionization rates were increased by four orders of magnitude in the PERMAX case, but the current sheet remained symmetric. However, the current sheet in the APHMIN case shifted slightly duskward when the ionization rates were decreased by nine orders of magnitude. It was determined that the crustal magnetic fields dominate the magnetotail current sheet shift, and the code setups from this investigation should be scrutinized for refined model comparison.