CO2 and Temperature Profiles in the Martian Atmosphere from Solar Occultation Measurements by Trace Gas Orbiter Instruments NOMAD and ACS

. Vertical profiles of CO2 and temperature with good vertical resolution are key measurements to characterize the Martian atmosphere, although difficult to obtain from remote observations [1]. For the first time these vertical profiles can be routinely obtained with a solar occultation technique by the instruments NOMAD/SO and ACS/MIR on board the Exomars Trace Gas Orbiter [2,3]. We will present data obtained in the 2.7 um region, dominated by a well known ro-vibrational band of CO2, and routinely sampled by both instruments using a mixture of diffraction orders, with the capability to sample the whole atmosphere, up to about 180 km. Before exploiting these instruments' datasets it is important to cross-validate their retrieval results and performace as accurately as possible. For this purpose we apply a flexible and well tested Earth atmosphere retrieval scheme [5,6,7], to both of them, after adaptation to Mars atmospheric conditions [4] and the necessary accomodation of these channels characteristics. The retrievals use calibrated transmittance spectra to tackle three targets, CO2 density, temperature, and dust loading, in a simultaneous global-fit inversion, with updated hydrostatic equilibrium in every iteration, including contaminant species like H2O. Synthetic retrievals were performed to optimize retrieval parameters, like regularization and vertical resolution, in a sequential estimator strategy,. The retrievals are performed after a pre-processing/data cleaning analysis which is instrument specific but sharing many similarities between the SO and MIR channels, like computing the optimal instrumental line shape or correcting for potential spectral bendings and shifts (see [8] for NOMAD/SO calibration details). The results from this study are intended to supply consistent inputs for retrievals of other atmospheric species in the same scan, wherever possible, like H2O and CO, and/or to build climatologies and validate climate models. Acknowledgement: The IAA/CSIC team acknowledges financial support from the State Agency for Research of the Spanish MCIU through the Center of Excellence Severo Ochoa award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709) and funding by grant PGC2018-101836-B-100 (MCIU/AEI/FEDER, EU). ExoMars is a space mission of the European Space Agency (ESA) and Roscosmos. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB-BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University). US investigators were supported by the National Aeronautics and Space Administration. References: [1] Lopez-Valverde et al., Space Sci Rev, 214, 29 (2018) [2] Vandaele et al., Space Science Reviews 214, 5, 2018 [3] Korablev et al., Space. Sci. Rev. 214, 7 (2018). [5] Funke, B., et al. , Atmos. Chem. Phys., 9(7), 23872411 (2009). [4] Jimenez-Monferrer et al., Icarus, 353, 113830 (2020), doi.org/10.1016/j.icarus.2020.113830. [6] Stiller et al., JQSRT, 72, 249280 (2002) [7] von Clarmann et al., J. Geophys. Res. 108, 4746 (2003) [8] Liuzzi et al. Icarus 321 (2019): 671-690.