Localized Hybrid Simulation of Martian Crustal Magnetic Cusp Regions: Vertical Electric Potential Drop and Plasma Dynamics

Abstract

AbstractThe localized crustal magnetic fields of Mars play an important role in the planet’s ionosphere‐solar wind interaction. Various physical processes in the induced magnetosphere, such as particle precipitation, field‐aligned currents, and ion outflow, are usually associated with the crustal magnetic cusp regions, where field lines are mostly vertical and open to space. Due to the small spatial scale (a few hundred km) of the Martian crustal magnetic cusps, localized models with high spatial resolutions and ion kinetics are needed to understand the physical processes. We adapt the simulation platform HYB developed at the Finnish Meteorological Institute to a moderately strong magnetic cusp above the Martian exobase with a 2‐D simulation domain assuming periodic boundary conditions on the third dimension. Two plasma sources are included in the simulation: hot protons from the induced magnetosphere and cold heavy ions (O+) from the ionosphere. Our model results can qualitatively reproduce the vertical electric potential drop, particle transport, and field aligned current in the cusp region. The vertical electric potential is built up mostly by the Hall electric field as a result of the separation between ion and electron fluxes of the downward plasma flow. By varying the model inputs, we found that the vertical potential drop depends on ionospheric ion density and magnetic field strength. These results tell us that energy is transferred from magnetospheric plasma to ionospheric plasma through the vertical electric potential buildup in magnetic cusps and how this process may affect electron precipitation, ion escape, and ionosphere conditions at Mars.