Mars Thermospheric Polar Warming at Aphelion: Dynamical Processes Studied Using M-GITM

Abstract

Aphelion Thermospheric Polar Warming (TPW), first identified in 2024 by Mars Atmosphere and Volatile EvolutioN (MAVEN) observations, is a dynamical heating phenomenon in the Martian atmosphere that exists in the winter hemisphere near the aphelion solstice. Studying the formation mechanism of aphelion TPW will help us better understand the energy budget of the Martian thermosphere. In this study, we investigate aphelion TPW using the Mars Global Ionosphere Thermosphere global circulation model (M-GITM). The simulation results show that the local dust storms have little impact on the formation of aphelion TPW. The simulated thermospheric temperature difference between the polar region and the low-latitude region is considerably lower than the value observed, which suggests that some important atmospheric processes are not captured by M-GITM. To investigate potential causes, we conduct sensitivity tests on solar insolation, gravity waves, and model horizontal resolution. The sensitivity test on solar insolation shows that the magnitude of aphelion TPW increases with increasing solar insolation. We also find that gravity waves play a critical role in modulating dynamical heating, as their suppression increases the latitudinal temperature difference. Model resolution has minimal impact on polar warming but affects thermospheric structure at low latitudes. These findings highlight the importance of refining the representation of dynamical processes, especially the parameterization of subgrid-scale internal gravity waves in the Martian general circulation model to better capture thermospheric dynamics.