Seasonal Variations and GlobalWave Distributions in the Mars Thermosphere From MAVEN and Multisatellites Accelerometer-Derived Mass Densities

摘要

Martian lower thermospheric variations are complex due to internal surface dust storms and external solar activities. However, limited Martian measurement data are restricted to observe and understand its variations in the past. In this paper, multisatellite accelerometer-derived densities and the Mars Climate Database are used to investigate seasonal variations, gravity waves, and coupling effects with the internal and external inputs, including Mars Global Surveyor, Mars Reconnaissance Orbiter, Mars Odyssey, and Mars Atmosphere and Volatile EvolutioN Mission. The diurnal and seasonal structures are reconstructed by the data, and the phase of the cycles is formed by solar heating/ionizing processes. Both amplitude and phase are impacted by surface dust activities during autumn and winter, for which density increases about 1.5-3.5 times compared to spring and summer seasons. A parameterized model that includes a newly introduced dust index is proposed to well fit and reinterpret the seasonal cycles. Furthermore, the coupling process between internal atmospheric gravity waves (IAGWs) and dust activities are investigated and explained. During dust storm times/seasons, the IAGWs exhibit both narrower amplitude peaks and deposit their energy at higher altitudes relative to "clear sky" times. The IAGWs could extend their energies into higher layers beyond exobase due to a thermospheric layer expansion (i.e., density increase) during dust seasons.