DOI: 10.7302/36zc-y350
title: Mars Thermospheric Helium Distributions:  M-GITM Simulated Datasets for Comparison to MAVEN/NGIMS Measurements

description: The NASA MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft, which is currently in orbit around Mars, has been taking systematic measurements of the densities and deriving temperatures in the upper atmosphere of Mars between about 140 to 240 km above the surface since late 2014. Wind measurement campaigns are also conducted once per month for 5-10 orbits. These densities, temperatures and winds change with time (e.g. solar cycle, season, local time) and location, and sometimes fluctuate quickly. Global dust storm events are also known to significantly impact these density, temperature and wind fields in the Mars thermosphere.

For the current project, the inert light species helium is used to trace the circulation patterns and constrain wind magnitudes throughout the Mars thermosphere. Presently, more than 6 years of Neutral Gas and Ion Mass Spectrometer (NGIMS) measurements of helium densities have been obtained by the MAVEN team (e.g. Elrod et al., 2017; 2021; Gupta et al., 2021). Measured helium distributions are compared to simulations from a computer model of the Mars atmosphere called M-GITM (Mars Global Ionosphere-Thermosphere Model), developed at U. of Michigan. Since the global circulation plays a role in the structure, variability, and evolution of the atmosphere, understanding the processes that drive the winds in the upper atmosphere of Mars also provides the needed context for understanding helium distributions and how the atmosphere behaves as a whole system.  

Three dimensional M-GITM simulations for the Mars four cardinal seasons (Ls = 0, 90, 180, 270, for Mars Year 33) were conducted for detailed comparisons with NGIMS helium and CO2 distributions (Gupta et al. 2021). The  M-GITM datacubes used to extract these densities (plus winds) along the trajectory of each orbit path between 140 and 240 km, are provided in this Deep Blue Data archive. README files are also provided for each datacube, detailing the contents of each file. In addition, a general README file is provided that summarizes the inputs and outputs of the M-GITM code simulations for this study. Finally, a basic version of the M-GITM code can be found on Github at  https:/github.com/dpawlows/MGITM.

description: Simulated neutral densities (CO2, CO, N2, O, Ar, O2, N, NO, including helium) and corresponding zonal, meridional and vertical neutral winds of the Mars thermosphere are calculated by the 3-D numerical model called M-GITM (Mars Global Ionosphere-Thermosphere Model), developed at the U. of Michigan. This is a climate model whose domain extends from the surface to ~250 km (Bougher et al., 2015). Neutral plus ion densities, neutral temperatures and winds are calculated on a 3-D grid (latitude, longitude, altitude) for NASA MAVEN spacecraft conditions corresponding to specific instrument measurements made. These 3-D model calculations are time-marching, making use of a finite-difference code which solves the Navier-Stokes equations for temperatures, composition, and winds. Large datacubes are created of M-GITM outputs fields for deposit on this archive