Localized Hybrid Simulation of Martian Crustal Magnetic Cusp Regions

Mars does not have a global dipole magnetic field, but has localized crustal fields, which play a role in the ionosphere and solar wind interaction. The Martian crustal fields are involved in various physical processes in the induced magnetosphere, such as particle precipitation, field-aligned currents, and ion outflow. These processes usually occur in the magnetic ‘cusp’ regions with mostly vertically aligned and open field lines. Due to the small spatial scale of the Martian crustal magnetic cusps, localized models with high spatial resolutions and ion kinetics are needed to understand the physical processes in the cusp regions.

We use the HYB hybrid simulation platform developed at the Finnish Meteorological Institute to model Martian magnetic cusp regions. We adapt the HYB model to a moderately strong magnetic cusp (surface magnetic field strength ~100 nT) on the nightside of Mars with a 2-D simulation domain using periodic field and particle distributions in the 3^rd dimension. Two plasma sources are included in the simulation: hot protons from the magnetotail and cold heavy ions from the ionosphere. Our model results can qualitatively reproduce the vertical electric potential drop, particle transport, and field aligned current in the cusp region, which provides a possible mechanism of the buildup of the vertical electric field and the energy transfer between the two plasma populations. We also run the model under different ionosphere and magnetic field conditions to study the variability of the cusp system and discuss the effects on the ion escape in the cusp region.