Comparing MAVEN/NGIMS Thermospheric Wind Observations with M-GITM Simulations

The Neutral Gas and Ion Mass Spectrometer (NGIMS) instrument on the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has been measuring winds in the Martian thermosphere in monthly campaigns since 2016. These unique observations - the first in-situ measurements of neutral wind velocities in the Martian thermosphere - have begun to provide a picture of the spatially and temporally variable upper atmospheric neutral flow. Comparing this set of observations to simulations from general circulation models (GCMs) allows for the relative importance of processes driving winds in the upper atmosphere of Mars to be investigated.

In this study, several NGIMS wind campaigns are compared to simulations from the Mars Global Ionosphere - Thermosphere Model (M-GITM), a 3-D ground to exosphere GCM. Characteristics of averaged wind profiles from selected campaigns are compared to wind profiles extracted from the model. In some campaigns the simulated winds replicate the observed winds reasonably well, while other campaigns show notable differences between observations and simulations in wind speed, direction, or both. M-GITM is currently primarily driven by solar forcing at thermospheric altitudes, including absorption of extreme ultraviolet (EUV) radiation, which is the primary heating mechanism in the thermosphere. Therefore, large discrepancies between simulations and observations suggest that, in these cases, mechanisms other than differential EUV heating are driving the neutral thermospheric winds. Furthermore, the relative importance of these other processes and normal solar forcing are seen to vary from campaign to campaign, at different local times and seasons.

The high variability and large discrepancies seen in some cases could correspond to effects of processes not included in M-GITM for these simulations, such as gravity waves. A spectral nonlinear gravity wave parameterization scheme is being added to M-GITM to identify the relative importance of the effects of gravity waves in conditions corresponding to these NGIMS wind campaigns.