A Comparative Analysis of Gravity Waves in He and Ar Densities in the Martian Thermosphere

Abstract

In this study, we conducted a comparative analysis of gravity waves (GWs) in the Martian upper thermosphere, utilizing He and Ar densities measured by the Neutral Gas and Ion Mass Spectrometer aboard the Mars Atmosphere and Volatile EvolutioN spacecraft. Our investigation revealed that GWs are a persistent phenomenon in Martian thermospheric He densities, akin to their presence in heavier species like Ar and CO2. Intriguingly, we observed that local time and seasonal variations in He GW amplitudes exhibit an almost opposite pattern compared to those in Ar. A significant breakthrough was the identification of a temperature‐dependent transition wavelength distinctly demarcating short and long wavelengths. This transition wavelength, which increases with increasing background temperatures, profoundly influences the dominance of GW amplitudes in He and Ar. In the short‐wavelength limit, GW amplitudes in He prevail, while GW amplitudes in Ar take precedence in the long‐wavelength limit. During periods of lower temperatures during midnight and the dawn terminator, transition wavelengths fall within the observed wavelength range enabling the study of dominance of GWs in He and Ar. Conversely, higher temperatures (>180 K) during daytime and the dusk terminator eliminate transition wavelengths within our observational range. Consequently, the amplitudes of GWs in He dominate over those in Ar. Furthermore, under nominal dust conditions, GWs in both He and Ar exhibit an inverse relationship with their respective background densities. During global dust storm, this inverse relationship is maintained for GWs in He, while GWs in Ar display a slight positive correlation with background Ar densities.