Zonal-Mean N₂ and Ar Densities and Temperatures in Mars Thermosphere From MAVEN

Abstract

Measurements of Ar and N₂ densities at 160–250 km altitude from the Mars Atmosphere and Volatile Evolution (MAVEN) Neutral Gas and Ion Mass Spectrometer (NGIMS) during February 2015–February 2023 are analyzed to provide a comprehensive analysis of their diurnal- and zonal-mean (DZM) structures, and ZM (solar-synchronous) diurnal (DW1) and semidiurnal (SW2) tides. After applying a solar flux trend correction, multi-year binning and averaging with respect to longitude, local solar time (LST), latitude and Ls at each height results in the first full global picture of these components of the ZM thermosphere for a single climatological Mars year. The following new observational insights into Mars thermosphere are obtained: The DZM N₂ latitude versus Ls (latvsLs) structures contain a prominent latitudinally-symmetric annual component (~±25%–35%) due to the eccentricity of Mars orbit around the Sun, and an antisymmetric component (~±30%–45%) below about 190 km that is seasonally-symmetric and thus consistent with the tilt of Mars rotation axis. Aperiodic deviations from these symmetries increase with height and are tentatively attributed to dissipation of waves originating in the lower atmosphere. DW1 and SW2 maximize around 200–220 km altitude, suggesting existence of an unknown dissipation mechanism at higher altitudes. The DZM, DW1 and SW2 components of Ar generally exceed those of N₂ by factors of 1.4–2.5. The scale heights of Ar and N₂ between 205 and 245 km are also employed to derive DZM exosphere temperatures, which reflect aperiodic ~±15K deviations from the annual-mean in the latvsLs frame.