Longitudinal Variations of Mars Thermosphere CO₂, Ar, N₂, and O Densities From MAVEN: Dependencies on Species Mass, Solar Flux, and Local Time

Abstract

Measurements of CO₂, Ar, N₂, and O densities between 150 and 200 km from the Mars Atmosphere and Volatile Evolution Neutral Gas and Ion Mass Spectrometer during February 2015 to February 2022 are analyzed to provide a comprehensive analysis of their longitudinal wavenumber k = 1, 2, and 3 components. Variations in density amplitudes (Aₖ) with solar flux are marginally detectable during this period. The Aₖ binned and averaged in latitude, local solar time and Ls are referenced to diurnal- and zonal-mean backgrounds in accord with how tides and stationary planetary waves (SPWs) are defined in theory and modeling. The resulting global Aₖ distributions are the interference patterns formed by superposition of diurnal tides, SPWs and/or semidiurnal tides; consequently, a simple dependence on species mass consistent with thermal expansion (diffusive equilibrium) that might exist for some individual wave components is obscured. Additionally, vertical winds likely contribute to deviations from diffusive equilibrium. Complementary analyses of the Mars Climate Database indicate that the major contributors to the Aₖ are DE2, SE1, DE1, and SPW1, 2, 3; support the absence of significant variability due to solar flux; and indicate a more well-defined sensitivity to species mass. The Aₖ and their phases (longitudes of maxima) for the whole data set are available as part of Supporting Information S1.