Seasonal variability of gravity wave activity in Mars's lower atmosphere from MGS–TES nadir observations

Abstract

Gravity waves (GW) in the lower atmosphere play an important part in Mars' atmospheric dynamics and energy balance, transferring momentum and energy to higher altitudes and affecting cloud formation. Gravity wave activity at the global scale on Mars can be studied from statistical analysis of variances of brightness temperatures observed by orbiting instruments. We use observations collected by the Thermal Emission Spectrometer (TES) aboard Mars Global Surveyor (MGS) during Mars Years 24–27 to explore spatial and seasonal variability of GW activity at horizontal scales ~100 km and on vertical scales >40 km. TES radiances were re-sampled to Mars Reconnaissance Orbiter (MRO) Mars Climate Sounder (MCS) spectral channels A1 (595–615 cm−1), A2 (615–645 cm−1) and A3 (635–665 cm−1) in the wings of the 15 μm CO2 band to sense GWs in the lower atmosphere. Results show that GW activity correlates with topographic roughness and is likely excited by orographic sources. GW activity decreases significantly with height, suggesting critical level filtering. During the global dust storm (GDS) of MY25 GW activity decreased substantially in the southern hemisphere. High levels of instrument noise that varied through the TES mission make it difficult to make a definitive statement about interannual variability in GW activity.