Morphological and dynamical analysis of Martian Gravity Waves using MEx/HRSC observations

Kurzfassung

Atmospheric gravity waves (AGWs) significantly influence Mars’ climate by facilitating energy and momentum exchanges, thus modulating atmospheric circulation, cloud formation, and dust distribution processes [1]. Despite recent advances in the characterization of Martian AGWs using observations from Mars Express/OMEGA [2], this study was limited by the narrow field of view and restricted spatial coverage. Here, we present an extended analysis using data from the High-Resolution Stereo Camera (HRSC) [3], likewise onboard Mars Express (MEx), benefiting from its higher spatial coverage, resolution (map scales between 200-800 m/px), and consistent imaging quality. We examined HRSC high-altitude imagery covering Mars Years (MY) 34-37 [4], identifying and characterizing over 100 distinct wave packets, nearly doubling the number previously analyzed. Our refined cloud-altitude measurement technique significantly improved the accuracy and robustness of cloud height retrievals, resulting in estimated altitudes of 15-40 km for water-ice clouds and 60–100 km for CO2-ice clouds, with uncertainties around ±2 km. Wind speeds were determined through precise cloud displacement analyses from HRSC double-broom imagery, taken with an interval of 30 minutes apart, consistently yielding values between 5-20 m/s and uncertainties of approximately ±1 m/s, though these uncertainties likely underestimate the total error due to unresolved spacecraft pointing inaccuracies. Additionally, by retrieving the wind speeds of wave packets and the background, we derived preliminary phase speed estimates for the detected wave packets. Comparison with local background winds suggests a range of intrinsic wave behaviours, which reflect differences in their generation mechanisms or propagation environments. Our enhanced dataset allows us to establish seasonal and spatial patterns of gravity wave occurrence, highlighting a prominent hemispheric asymmetry with significantly more wave observations in the northern hemisphere. This raises new questions about observational biases potentially related to spacecraft observational strategies. Additionally, the measured wind speeds remain consistently lower than mesoscale model predictions from the Mars Climate Database [5,6], suggesting that current atmospheric models may inadequately represent mesoscale dynamics associated with gravity waves. Collaborations with the OMEGA and TGO/CaSSIS teams are now extending this analysis further, incorporating spectral information for cloud composition (OMEGA) and complementary observational geometries (CaSSIS), crucial for addressing the limitations identified in this work. These multi-instrument synergies will allow better discrimination of physical processes involved in wave formation, propagation, and dissipation. This comprehensive analysis using HRSC data provides critical insights into Martian atmospheric dynamics, which can be used to improve current atmospheric models using the parameterization of gravity waves characterized in this work.