Variations of the Martian plasma environment during the ICME passage on 8 March 2015: A time-dependent MHD study

The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft observed astrong interplanetary coronal mass ejection (ICME) impacting Mars on 8 March 2015. We use a time-dependent global MHD model to investigate the response of the Martian ionosphere and induced magnetosphere to the large solar wind disturbance associated with the ICME. Taking observed upstream solar wind conditions from MAVEN as inputs to the MHD model, the variations of the Martian plasma environments are simulated realistically in a time period from 2.5 h prior to the arrival of the ICME shock to about 12 h after the impact. Detailed comparisons between the model results and the relevant MAVEN plasma measurements are presented, which clearly show that the time-dependent multispecies single-fluid MHD model is able to reproduce the main features observed by the spacecraft during the ICME passage. Model results suggest that the induced magnetosphere responds to solar wind variation on a very short time scale (approximately minutes). The variations of the plasma boundaries' distances from the planet along the subsolar line are examined in detail, which show a clear anticorrelation with the magnetosonic Mach number. Plasma properties in the ionosphere (especially the induced magnetic field) varied rapidly with solar wind changes. Model results also show that ion escape rates could be enhanced by an order of magnitude in response to the high solar wind dynamic pressure during the ICME event.