Characterising Atmospheric Gravity Waves on Mars using Mars Express OMEGA images – novel results from systematised study

<p><span data-preserver-spaces="true">Atmospheric gravity waves are mesoscale atmospheric oscillations in which buoyance acts as the restoring force, being a crucial factor in the circulation of planetary atmospheres since they transport momentum and energy, which can dissipate at different altitudes and force the dynamics of several layers of the atmosphere [1]. The source of these waves can be associated with the topographic features (orographic gravity waves) of surface, or with jet streams and atmospheric convection (non-orographic gravity waves). Recent modelling studies showed the strong role of gravity waves on diurnal tides on Mars atmosphere [2], however their characteristics are still not well constrained by observations.</span></p> <p><span data-preserver-spaces="true">Here we report follow-up results from the detection and charaterisation of atmospheric waves on Mars&#8217; atmosphere, using data from the OMEGA spectrometer onboard the Mars Express (MEx) space mission [3]. We used image navigation and processing techniques based on contrast enhancement and geometrical projections to characterise morphological properties of the detected waves.</span></p> <p><span data-preserver-spaces="true">Our observations include the MEx nominal mission of the OMEGA instrument for the Martian years 27 and 28 (from January 2004 &#8211; January 2006 and from June &#8211; July 2007), constituted by 27 orbits and 4072 hyperspectral data QUBES. Every image was navigated and processed in order to optimise the detection of the wave packets and accurate characterisation of the wave properties such as the horizontal wavelength, packet width, packet length and orientation. The characterised wave-packets present a wide range of properties over a broad region of Mars&#8217; globe specially in the evolution of gravity waves along the time. We also found that the detected waves occur at solar longitudes between 240-250&#186; and 330-340&#186;, which almost corresponds to the beginning and the end of the dust storm seasons. This preliminary result suggest a relationship between the presence of atmospheric waves and the dust storm events, already mentioned by Gondet et al. (2019).</span></p> <p><span data-preserver-spaces="true">&#160;</span></p> <p><span data-preserver-spaces="true">&#160;</span><span data-preserver-spaces="true">&#160;</span></p> <p><strong><span data-preserver-spaces="true">Acknowledgements</span></strong><span data-preserver-spaces="true">: We acknowledge support from the Portuguese Funda&#231;&#227;o Para a Ci&#234;ncia e a Tecnologia of reference PTDC/FIS-AST/29942/2017, through national funds and by FEDER through COMPETE 2020 of reference POCI-01-0145-FEDER-007672, and through a grant of reference 2021.05455.BD. Funded by ESA Faculty research contract and Science Exchange Programme in the frame of MWWM - Mars Wind and Wave Mapping project.</span><span data-preserver-spaces="true">&#160;We would like to thank the late Dr Brigitte Gondet for her considerable help that made this work possible.</span></p> <p><span data-preserver-spaces="true">&#160;</span></p> <p><strong>References</strong></p> <p><span data-preserver-spaces="true">[1] Fritts, D. C.; Alexander, M. J. Gravity wave dynamics and effects in the middle atmosphere.&#160;</span><em><span data-preserver-spaces="true">Reviews of geophysics</span></em><span data-preserver-spaces="true">, 2003, 41.1.</span></p> <p><span data-preserver-spaces="true">[2] Gilli, G., et al. Impact of gravity waves on the middle atmosphere of Mars: A non&#8208;orographic gravity wave parameterization based on global climate modeling and MCS observations.&#160;</span><em><span data-preserver-spaces="true">Journal of Geophysical Research: Planets</span></em><span data-preserver-spaces="true">, 2020, 125.3: e2018JE005873.</span></p> <p><span data-preserver-spaces="true">[3] Brasil, Francisco, et al. Characterising Atmospheric Gravity Waves on Mars using Mars Express OMEGA images&#8211;a preliminary study. In:&#160;</span><em><span data-preserver-spaces="true">European Planetary Science Congress</span></em><span data-preserver-spaces="true">. 2021. p. EPSC2021-188.</span></p> <p><span data-preserver-spaces="true">[4] Gondet and J.-P. Bibring. Mars observations by omega/mex during the dust events from 2004 to 2019. In&#160;</span><em><span data-preserver-spaces="true">EPSC-DPS Joint Meeting 2019</span></em><span data-preserver-spaces="true">, volume 2019, pages EPSC&#8211;DPS2019, 2019.</span></p>