[1] We present the extension to the thermosphere of a Martian general circulation model, the first able to self-consistently study the whole Martian atmosphere from the surface to the exosphere. We describe the parameterizations developed to include physical processes important for thermospheric altitudes. The results of a simulation covering 1 full Martian year are presented, focusing on the seasonal, diurnal, and day-to-day variability of the temperatures in the exobase region. The seasonal variation of the zonal mean temperatures in the upper atmosphere is of about 100 K, mostly due to the variation of the solar forcing. The temperature of the mesopause ranges between 115 and 130 K, with little seasonal and day-night variations. Its pressure level undergoes significant seasonal and day-night variations. Comparisons with SPICAM observations show that the modeled mesopause is too low and too warm. A similar study for the homopause shows that it is located higher in the atmosphere during solstices, owing to reinforced mixing by a stronger circulation. Important day-night temperature differences are found in the thermosphere, ranging from about 60 K at aphelion to 110 K at perihelion. This diurnal cycle is slightly perturbed by the day-to-day variations of temperature, dominated by waves with periods of 2 to 6 sols and amplitude of 30 K. The model reproduces the observed solar cycle variation in temperatures when using a UV heating efficiency of 16%, slightly lower than the theoretical value. The seasonal variation of temperatures is overestimated by the model, in comparison with the available measurements.

<p class="western" lang="en-US" align="justify"><strong>Introduction:</strong></p> <p class="western" lang="en-US" align="justify">The Mars Climate Database (MCD) is a database of meteorological fields derived from General Circulation Model (GCM) numerical simulations of the Martian atmosphere and validated using available observational data. The MCD includes complementary post-processing schemes such as high spatial resolution interpolation of environmental data and means of reconstructing the variability thereof.</p> <p class="western" lang="en-US" align="justify">The GCM that is used to create the MCD data, now known as the Mars Planetary Climate Model (Mars PCM) is developed at Laboratoire de Météorologie Dynamique du CNRS (Paris, France) [1] in collaboration with LATMOS (Paris, France), the Open University (UK), the Oxford University (UK) and the Instituto de Astrofisica de Andalucia (Spain) with support from the European Space Agency (ESA) and the Centre National d'Etudes Spatiales (CNES).</p> <p class="western" lang="en-US" align="justify">The latest version of the MCD, version 5.3 [2], was released in July 2017, and at the time of writing of this abstract we are working on MCDv6.1 [3], which we will release in June 2022. This new version will benefit from all the recent developments and improvements in the Mars PCM’s physics package.</p> <p class="western" lang="en-US" align="justify">The MCD is freely distributed and intended to be useful and used in the framework of engineering applications as well as in the context of scientific studies which require accurate knowledge of the state of the Martian atmosphere. Over the years, various versions of the MCD have been released and handed to more than 400 teams around the world.</p> <p class="western" lang="en-US" align="justify">Current applications include entry descent and landing (EDL) studies for future missions, investigations of some specific Martian issues (via coupling of the MCD with homemade codes), analysis of observations (Earth-based as well as with various instruments onboard Mars Express, Mars Reconnaissance Orbiter, Maven, Trace Gas Orbiter, Hope),...</p> <p class="western" lang="en-US" align="justify">The MCD is freely available upon request via an online form on the dedicated website: http://www-mars.lmd.jussieu.fr which moreover includes a convenient web interface for quick looks.</p> <p class="western" lang="en-US" align="justify"><img src="" alt="" /></p> <p class="western" lang="en-US" align="justify"><strong>Figure 1</strong>: Illustrative example of the online Mars Climate Database web interface and its plotting capabilities.</p> <p class="western" lang="en-US" align="justify"><strong>Overview of MCD contents:</strong></p> <p class="western" lang="en-US" align="justify">The MCD provides mean values and statistics of the main meteorological variables (atmospheric temperature, density, pressure and winds) as well as atmospheric composition (including dust and water vapor and ice content), as the GCM from which the datasets are obtained includes water cycle, chemistry, and ionosphere models. The database extends up to and including the thermosphere (~350km). Since the influence of Extreme Ultra Violet (EUV) input from the sun is significant in the latter, 3 EUV scenarios (solar minimum, average and maximum inputs) account for the impact of the various states of the solar cycle.</p> <p class="western" lang="en-US" align="justify">As the main driver of the Martian climate is the dust loading of the atmosphere, the MCD provides climatologies over a series of synthetic dust scenarios: standard year (a.k.a. climatology), cold (i.e: low dust), warm (i.e: dusty atmosphere) and dust storm, These are derived from home-made, instrument-derived (TES, THEMIS, MCS, MERs), dust climatology of the last 12 Martian years. In addition, we also provide additional “add-on” scenarios which focus on individual Martian Years (from MY 24 to MY 35) for users more interested in more specific climatologies than the MCD baseline scenarios.</p> <p class="western" lang="en-US" align="justify">In practice the MCD provides users with:</p> <ul> <li class="western" lang="en-US"> <p class="western" lang="en-US" align="justify">Mean values and statistics of main meteorological variables (atmospheric temperature, density, pressure and winds), as well as surface pressure and temperature, CO2 ice cover, thermal and solar radiative fluxes, dust column opacity and mixing ratio, [H20] vapor and ice concentrations, along with concentrations of many species: [CO], [O2], [O], [N2], [Ar], [H2], [O3], [H] ..., as well as electrons mixing ratios. Column densities of these species are also given.</p> </li> <li class="western" lang="en-US">Physical processes in the Planetary Boundary Layer (PBL), such as PBL height, minimum and maximum vertical convective winds in the PBL, surface wind stress and sensible heat flux.</li> <li class="western" lang="en-US"> <p class="western" lang="en-US" align="justify">The possibility to reconstruct realistic conditions by combining the provided climatology with additional large scale (derived from Empirical Orthogonal Functions extracted from the GCM runs) and small scale perturbations (gravity waves).</p> </li> <li class="western" lang="en-US"> <p class="western" lang="en-US" align="justify">Dust mass mixing ratio, along with estimated dust effective radius and dust deposition rate on the surface are provided.</p> </li> <li class="western" lang="en-US"> <p class="western" lang="en-US" align="justify">A high resolution mode which combines high resolution (32 pixel/degree) MOLA topography records and Insight pressure records with raw lower resolution GCM results to yield, within the restriction of the procedure, high resolution values of atmospheric variables (pressure, but also temperature and winds via dedicated schemes).</p> </li> </ul> <p> </p> <p class="western" lang="en-US" align="justify"><strong>Validation of</strong><strong> MCDv6.1:</strong></p> <p class="western" lang="en-US" align="justify">At EPSC2022 we will present validation campaigns between the MCDv6.1 and multiple measurements such as:</p> <ul> <li class="western" lang="en-US"> <p class="western" lang="en-US" align="justify">Surface temperatures, atmospheric temperatures and water vapor from TES/MGS.</p> </li> <li class="western" lang="en-US"> <p class="western" lang="en-US" align="justify">Atmospheric temperatures, water ice and airborne dust from MCS/MRO.</p> </li> <li class="western" lang="en-US"> <p class="western" lang="en-US" align="justify">Atmospheric temperatures from MGS and MEx radio occultations</p> </li> <li class="western" lang="en-US"> <p class="western" lang="en-US" align="justify">Atmospheric temperatures from TIRVIM/ACS/TGO</p> </li> <li class="western" lang="en-US"> <p class="western" lang="en-US" align="justify">Surface pressures recorded by Viking Landers, Phoenix, Curiosity and Insight</p> </li> <li class="western" lang="en-US"> <p class="western" lang="en-US" align="justify">And hopefully much more...</p> </li> </ul> <p> </p> <p class="western" lang="en-US" align="justify"><strong>References:</strong></p> <p class="western" lang="en-US" align="justify">[1] Forget et al. (2022), <span lang="fr-FR">“Challenges in Mars Climate Modelling with the LMD Mars Global Climate Model, Now Called the Mars « Planetary Climate Model »(PCM) “, The 7th International Workshop on the Mars Atmosphere : Modelling and Observations, 14-17 June 2022, Paris, France.</span></p> <p class="western" lang="en-US" align="justify"><span lang="fr-FR">[2] Millour et al. </span>(2018), “The Mars Climate Database (version 5.3) “, From Mars Express to ExoMars Scienfic Workshop, 22-28 February 2018, ESAC Madrid, Spain.</p> <p class="western" lang="en-US" align="justify"><span lang="fr-FR">[3] </span><span lang="fr-FR">Millour et al. (2022), “The Mars Climate Database, Version 6.1 “, The 7th International Workshop on the Mars Atmosphere : Modelling and Observations, 14-17 June 2022, Paris, France.</span></p>

To study the transport of the ionospheric plasma on Mars, we have included a 3-D multifluid dynamical core in a Martian general circulation model. Vertical transport modifies the ion density abovẽ 160 km on the dayside, especially the ions produced at high altitudes like O + , N + , and C + . Near the exobase, the dayside to nightside flow velocity reaches few hundreds of m/s, due to a large horizontal pressure gradient. Comparison with Mars Express/Analyzer of Space Plasmas and Energetic Atoms-3 measurements between 290 and 500 km suggests that this flow could account for at least 20% of the flow produced by the solar wind. This flow is not sufficient to populate substantially the nightside ionosphere at high altitudes, in agreement with recent observations, because of a strong nightside downward flow produced by vertical pressure gradient. The O 2 + and NO + ion densities on the nightside at low altitudes (~130 km) are modified by this downward flow, compared to simulated densities without ion dynamics, while other ions are lost by chemical reactions. Variability at different time scales (diurnal, seasonal, and solar cycles) are studied. We simulate diurnal and seasonal variations of the ionospheric composition due to the variability of the neutral atmosphere and solar flux at the top of the atmosphere. The ionospheric dynamics are not strongly affected by seasons and solar cycles, and the retroaction of the ionosphere on the neutral atmosphere temperature and velocity is negligible compared to other physical processes below the exobase.

[1] Many independent measurements have shown that extremely cold temperatures are found in the Martian mesosphere. These mesospheric "cold pockets" may result from the propagation of atmospheric waves. Recent observational achievements also hint at such cold pockets by revealing mesospheric clouds formed through the condensation of CO 2 , the major component of the Martian atmosphere. Thus far, modeling studies addressing the presence of cold pockets in the Martian mesosphere have explored the influence of large-scale circulations. Mesoscale phenomena, such as gravity waves, have received less attention. Here we show through multiscale meteorological modeling that mesoscale gravity waves could play a key role in the formation of mesospheric cold pockets propitious to CO 2 condensation.

[1] Limb observations with the SPICAM ultraviolet spectrometer on board the Mars Express orbiter revealed ultraviolet nightglow emission in the d (190-240 nm) and g (225-270 nm) bands of nitric oxide. This emission arises from radiative recombination between O( 3 P) and N( 4 S) atoms that are produced on the day side and form excited NO molecules on the night side. In this study, we analyze the night limb observations obtained during the MEX mission. In particular, we describe the variability of the emission brightness and its peak altitude. We examine possible correlations with latitude, local time, magnetic field strength or solar activity. We show that the altitude of maximum emission varies between 55 and 92 km while the brightness is in the range 0.2 to 10.5 kR. The total vertical emission rate ranges from 8 to 237 R with an average value of 36 ± 52 R. The observed topside scale height of the emission profile varies between 3.8 and 11.0 km, with a mean value of 6 ± 1.7 km. We use a chemical-diffusive atmospheric model where the eddy coefficient, whose value in the Mars thermosphere is uncertain, is a free parameter to match the observed peak altitude of the emission. The model solves the continuity equation for O( 3 P), N( 4 S), and NO using a finite volume method on a one-dimensional grid. We find that the downward flux of N atoms at 100 km varies by two orders of magnitude, ranging from 10 7 to 10 9 atoms cm À2 s À1 .