Solar wind interaction with the Martian upper atmosphere: Crustal field orientation, solar cycle, and seasonal variations

A comprehensive study of the solar wind interaction with the Martian upper atmosphere is presented. Three global models: the 3‐D Mars multifluid Block Adaptive Tree Solar‐wind Roe Upwind Scheme MHD code (MF‐MHD), the 3‐D Mars Global Ionosphere Thermosphere Model (M‐GITM), and the Mars exosphere Monte Carlo model Adaptive Mesh Particle Simulator (M‐AMPS) were used in this study. These models are one‐way coupled; i.e., the MF‐MHD model uses the 3‐D neutral inputs from M‐GITM and the 3‐D hot oxygen corona distribution from M‐AMPS. By adopting this one‐way coupling approach, the Martian upper atmosphere ion escape rates are investigated in detail with the combined variations of crustal field orientation, solar cycle, and Martian seasonal conditions. The calculated ion escape rates are compared with Mars Express observational data and show reasonable agreement. The variations in solar cycles and seasons can affect the ion loss by a factor of ∼3.3 and ∼1.3, respectively. The crustal magnetic field has a shielding effect to protect Mars from solar wind interaction, and this effect is the strongest for perihelion conditions, with the crustal field facing the Sun. Furthermore, the fraction of cold escaping heavy ionospheric molecular ions [(2+ and/or 2+)/Total] are inversely proportional to the fraction of the escaping (ionospheric and corona) atomic ion [O+/Total], whereas 2+ and 2+ ion escape fractions show a positive linear correlation since both ion species are ionospheric ions that follow the same escaping path.Key PointsStudy crustal field, solar cycle, and seasons on Mars' upper atmosphere ion escapeTo understand the long‐term evolution of Mars atmosphere over its historyTo support MAVEN spacecraft mission data analysis (2014–2016)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/115901/1/jgra52040.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/115901/2/jgra52040_am.pd

MAVEN/NGIMS thermospheric neutral wind observations: Interpretation using the M‐GITM general circulation model

Using a new observational technique, the NGIMS (Neutral Gas and Ion Mass Spectrometer) instrument on the MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft has the unique capability to measure horizontal thermospheric winds. Measured along the orbit track from periapsis (∼150 km) to ∼200 km, these are the first in situ observations of thermospheric winds at Mars. Significantly, this also means that simulated winds from a global circulation model can be compared to in situ observations from this part of the Martian atmosphere for the first time. In this study, observations from five NGIMS neutral wind campaigns have been compared to simulations from the Mars Global Ionosphere-Thermosphere Model (M-GITM), a ground to exosphere 3-D general circulation model. By comparing NGIMS neutral wind observations to model simulations, the processes driving the winds and their variations in the upper atmosphere are examined. These comparisons show that for certain observational periods, the M-GITM simulated winds can generally replicate the magnitude and/or direction of the NGIMS wind observations, while in others, significant differences occur. In general, wind observations from NGIMS campaigns with large orbit-to-orbit variability are not well replicated by M-GITM, while campaigns with higher observed wind speeds are better captured by the model. Additionally, using these data-model comparisons, the relative role of normal solar forcing and corresponding differential heating in driving thermospheric winds at Mars is found to be variable, likely acting as the primary driver under some conditions and secondary to other physical processes under others