Gravity waves in the thermosphere of Mars are complex and variable phenomena capable of causing significant changes to processes in the upper atmosphere of Mars, which can affect atmospheric escape. The objective of this study is to determine how both dust storm activity and variation in Local Solar Time (LST) affect thermospheric gravity wave activity. Analyzing in-situ neutral Argon density data from the Mars Atmospheric and Volatile EvolutioN (MAVEN) satellite’s Neutral Gas and Ion Mass Spectrometer (NGIMS), we measure the strength of the gravity wave activity across five nightside observation datasets in a variety of dust conditions: three outside of the Martian Dust season with nominal, low dust conditions, one during the 2018 Global Dust Storm (GDS), and one during the regional C storm observed in Mars Year (MY) 34. From nominal conditions, we find thermospheric gravity wave activity increases on the nightside, as seen in previous studies, but is twice as high post-midnight as it is pre-midnight. During the 2018 GDS, the thermospheric gravity wave activity observed between 22:00 and 06:00 LST is generally consistent with gravity wave activity observed during nominal dust conditions. Between 18:00 and 22:00, however, gravity wave activity during the 2018 GDS is ~7 times higher than the weak activity seen during these LSTs in nominal dust conditions. A similar effect is observed during the MY 34 regional C storm, during which gravity wave activity increased in step with the global dust loading.

Martian sub-solar electron temperatures obtained below 250 km are examined using data obtained by instruments on the Mars Atmosphere Evolution Mission (MAVEN) during the three sub-solar deep dip campaigns and a one-dimensional fluid model. This analysis was done because of the uncertainty in MAVEN low electron temperature observations at low altitudes and the fact that the Level 2 temperatures reported from the MAVEN Langmuir Probe and Waves (LPW) instrument are more than 400 Kelvin above the neutral temperatures at the lowest altitudes sampled (~120 km). These electron temperatures are well above those expected before MAVEN was launched. We find that an empirical normalization parameter, neutral pressure divided by local electron heating rate, organized the electron temperature data and identified a similar altitude (~160 km) and time scale (~2,000 s) for all three deep dips. We show that MAVEN data are not consistent with a plasma characterized by electrons in thermal equilibrium with the neutral population at 100 km. Because of the lack data below 120 km and the uncertainties of the data and the cross sections used in the one dimensional fluid model above 120 km, we cannot use MAVEN observations to prove that the electron temperature converges to the neutral temperature below 100 km. However, the lack of our understanding the electron temperature altitude profile below 120 km does not impact our understanding of the role of electron temperature in determining ion escape rates because ion escape is determined by electron temperatures above 180 km.

Lower atmospheric global dust storms affect the small- and large-scale weather and variability of the whole Martian atmosphere. Analysis of the CO2 density data from the Neutral Gas and Ion Mass Spectrometer instrument (NGIMS) on board NASA’s Mars Atmosphere Volatile EvolutioN (MAVEN) spacecraft show a remarkable increase of GW-induced density fluctuations in the thermosphere during the 2018 major dust storm with distinct latitude and local time variability. The mean thermospheric GW activity increases by a factor of two during the storm event. The magnitude of relative density perturbations is around 20% on average and 40% locally. One and a half months later, the GW activity gradually decreases. Enhanced temperature disturbances in the Martian thermosphere can facilitate atmospheric escape. For the first time, we estimate that, for a 20% and 40% GW-induced disturbances, the net increase of Jeans escape flux of hydrogen is a factor of 1.3 and 2, respectively.