Dust Storm Influence on Gravity Wave Activity in the Nightside Thermosphere of Mars

Abstract

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 dust storm activity, variation in Local Solar Time (LST), and seasonal changes 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) using a new metric called Mean Integrated Wave Power (MIWP), we measure the strength of the gravity wave activity across five nightside observation data sets (each of $\sim$300 orbits) in a variety of dust conditions: three outside of the Martian Dust season with low dust conditions, one during the 2018 Global Dust Storm (GDS), and one during the regional C storm observed in Mars Year (MY) 34. During nominal, low-dust conditions, we find the MIWP metric, and thereby gravity wave activity, is twice as high post-midnight as pre-midnight. This diurnal behavior is seen here first after L_s = $180°$. During the 2018 GDS, MIWP at 18:00–22:00 LST is higher when compared to dust-free conditions, consistent with past studies. However, MIWP at 22:00–06:00 LST is not statistically different from MIWP during low dust activity, suggesting that dust storm-driven variation in gravity wave activity is secondary to diurnal effects. MIWP during the MY34 regional C storm point toward 2 novel findings: seasonal variation in gravity wave activity and a strong correlation between dust loading and thermospheric gravity wave activity.