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We assimilate atmospheric temperature profiles and column dust optical depth observations from the ExoMars Trace Gas Orbiter Atmospheric Chemistry Suite thermal infrared channel (TIRVIM) into the Mars Planetary Climate Model. The assimilation period is Mars Year 34 Ls = 182.3°–211.4°, covering the onset and peak of the 2018 global dust storm. We assimilated observations using the Local Ensemble Transform Kalman Filter with 36 ensemble members and adaptive inflation; our nominal configuration assimilated TIRVIM temperature profiles to update temperature and dust profiles, followed by dust column optical depths to update the total column dust abundance. The observation operator for temperature used the averaging kernels and prior profile from the TIRVIM retrievals. We verified our analyses against in‐sample TIRVIM observations and independent Mars Climate Sounder (MCS) temperature and dust density‐scaled opacity profiles. When dust observations were assimilated, the root‐mean‐square temperature error verified against MCS fell by 50% during the onset period of the storm, compared with assimilating temperature alone. At the peak of the storm the analysis reproduced the location and magnitude of the peak in the nighttime MCS dust distribution, along with the surface pressure diurnal cycle measured by Curiosity with a bias of less than 10 Pa. The analysis winds showed that, at the peak of the storm, the meridional circulation strengthened, a 125 m s−1 asymmetry developed in the midlatitude zonal jets, the diurnal tide weakened near the equator and strengthened to 10–15 K at midlatitudes, and the semi‐diurnal tide strengthened almost everywhere, particularly in the equatorial lower atmosphere. Plain Language Summary: ExoMars Trace Gas Orbiter has been in low orbit around Mars since early 2018. During 2018 a large amount of dust was lifted from Mars' surface into the atmosphere. This eventually obscured most of the planet, forming a global dust storm. These storms have a large effect on the temperature and weather in Mars' atmosphere. We used observations from the spacecraft's thermal infrared instrument. This measures how much light comes from the atmosphere and surface at wavelengths where heat is emitted, and can be used to work out the atmospheric temperature and dust content at different times of day. We combined these observations with a numerical model of Mars' atmosphere, considering uncertainties in the measured atmospheric properties and the modeled atmosphere. We compared our results with temperature and dust observations made by Mars Climate Sounder on board Mars Reconnaissance Orbiter. Including dust observations was better than just using temperature observations. While the dust storm was raging, north‐south wind speeds increased, the strong eastward wind in the northern hemisphere became much stronger than in the southern hemisphere, and differences between day and night became larger. Our results mean we can better understand aspects of Mars' atmosphere throughout the daily cycle. Key Points: We assimilate temperature and dust observations from ExoMars Trace Gas Orbiter‐Atmospheric Chemistry Suite‐TIRVIM during the MY34 global dust storm (GDS)The analysis verifies well against independent Mars Climate Sounder temperature and dust profiles, and Curiosity pressure measurementsAt the peak of the GDS the winds strengthen, the diurnal tide migrates poleward, and the semi‐diurnal tide strengthens [ABSTRACT FROM AUTHOR]

The deuterium to hydrogen (D/H) ratio is commonly used to investigate the history of water on Mars, yet the mechanisms controlling present‐day HDO behavior are poorly understood. Significant variations of the D/H ratio were first predicted on the basis of a 3D global climate model, which were later confirmed by ground‐based observations. This behavior, consisting of lower HDO/H2O ratios in the colder regions of Mars, is related to the isotopic fractionation occurring at condensation. We leverage this previous effort and present an updated implementation, using the modern version of the model, that remains in agreement with the older version. We explore the impact of the global dust storm (GDS) that occurred during Martian year 34 (MY34) on HDO. Our simulations indicate that HDO is on average 40% more abundant at 100 km during the MY34 GDS year than during a regular year, with likely large consequences for the escape flux of water that year. Plain Language Summary: HDO, the semi‐heavy isotope of water, when compared to water, is a good indicator of how much water has been escaping from the atmosphere of Mars over the ages. Ultimately, it can be used to estimate the past reservoir of water available on Mars in its early youth. Because HDO has a slightly higher molecular mass compared to H2O, condensation induces an enrichment of HDO in the ice phase compared with the vapor phase. This subsequently causes spatial and temporal variations of the deuterium to hydrogen ratio. We use a global circulation model to simulate the HDO cycle in the atmosphere. Our model is an upgrade of the previous model presented in Montmessin et al. (2005, Journal of Geophysical Research, 110(E3), E10004. doi:10.1029/2004JE002357). We then simulate the effect of the global dust storm that affected Mars during the summer of 2018, and show that it should have had a strong impact on the vertical distribution of HDO, allowing it to reach higher altitudes. Such simulations are intended to be compared with observations from the Trace Gas Orbiter, currently in orbit around Mars. Key Points: We reimplemented the HDO cycle in a more recent version of the Laboratoire de Météorologie Dynamique Mars global climate modelWe reproduce the observed gradient of the deuterium to hydrogen ratio between cold and warm regionsThe global dust storm of Martian year 34 has a strong effect on the vertical distribution of HDO [ABSTRACT FROM AUTHOR]

We report a new water‐ice cloud feature observed during the Mars year 34 global dust storm: twilight cloud bands that routinely formed just past the evening terminator. We use images taken by the MAVEN/IUVS instrument. These bands were often latitudinally continuous, spanning over 6,000 km and were present between 18:00 and 19:00 local time. They were present for nearly the entire time IUVS imaged the evening terminator and often reached altitudes of at least 40 to 50 km during the mature phase of the storm. We compare these observations to LMD global climate model simulations. The simulations generally contain the temporal and spatial extents of the bands seen in IUVS data throughout the storm, but there are some discrepancies. We infer that these clouds formed as a result of semidiurnal thermal tides. Plain Language Summary: Water‐ice clouds and dust are among the most common particles in the Martian atmosphere, but the effect of global dust storms on cloud formation is largely unknown. We observed cloud bands that repeatedly formed near dusk during the Mars year 34 global dust storm. We saw these bands throughout the storm at locations all across the planet. We investigate this feature by using a global climate model, which predicted the formation of these cloud bands as a result of rapidly changing temperatures. The simulations of the bands contain several features seen in our observations, but not all. Key Points: We observed a new cloud formation phenomenon just after sunset during the Mars year 34 global dust storm in MAVEN/IUVS imagesGlobal climate model simulations are able to reproduce several but not all aspects of our observationsThese twilight clouds formed due to semidiurnal thermal tides [ABSTRACT FROM AUTHOR]

We report observations by the Mars Climate Sounder showing strong diurnal variations in temperature and the vertical dust distribution during the 2018 (Mars Year 34) global dust event. The temperature field shows weak diurnal tidal activity at equatorial latitudes but a strong diurnal tide in middle to high latitudes with a maximum amplitude of 29 K in the lower atmosphere of the south polar region. The diurnal variability of dust is small in the equatorial region and increases toward higher latitudes. At middle and low latitudes, comparable dust amounts are found about 5–10 km higher in the atmosphere on the dayside than on the nightside. The dust reaches the highest altitudes in the late afternoon and is found at the lowest altitudes in the late night. In the southern high latitudes a persistent cold air mass with low dust content is identified on the nightside of the planet centered at 3–6 a.m. local time. The observed variations are well represented by model simulations with the Laboratoire de Météorologie Dynamique General Circulation Model. Comparisons between data and model results suggest that the diurnal variations in the dust are largely driven by the meridional circulation exhibiting diurnal tidal variations. The model results show that the compact air mass in the south polar region has a high potential vorticity, supporting its interpretation as a remnant of the southern polar vortex, which is forced toward the nightside of the planet due to the enhanced diurnal tide during the global dust event. Plain Language Summary: One of the most distinctive features of the Martian atmosphere are global dust storms, one of which occurred in 2018. We report on observations of the vertical structure of atmospheric temperature and dust by the Mars Climate Sounder onboard Mars Reconnaissance Orbiter. Strong differences between day and night are found in both temperature and dust vertical structure. The strongest temperature variations are observed in the south polar atmosphere, with temperature differences up to 58 °C/136 °F between day and night. Comparable dust amounts are found 5–10 km (3–6 miles) higher in the atmosphere on the dayside than on the nightside at central and equatorial latitudes. In the southern polar region a persistent cold body of air with low dust is identified on the nightside of the planet. The observations are compared with the results from a global atmospheric computer model. The observed temperature and dust distribution and their variations over the Martian day are well represented by the model. The diurnal variations in the dust are largely driven by diurnal changes in the large‐scale atmospheric circulation. The compact body of air in the south polar region is forced to the nightside by this altered circulation but does not dissipate for several months. Key Points: The Mars Climate Sounder observes strong diurnal variations in the vertical distribution of dust during the 2018 global dust stormDust diurnal variability at low and middle latitudes is largely related to the meridional circulation exhibiting diurnal tidal variationsDiurnal variations at south polar latitudes are related to a remnant of the polar vortex confined to the nightside of the planet [ABSTRACT FROM AUTHOR]

Our Global Circulation Model (GCM) simulates the atmospheric environment of Mars. It is developped at LMD (Laboratoire de Meteorologie Dynamique, Paris, France) in close collaboration with several teams in Europe (LATMOS, France, University of Oxford, The Open University, the Instituto de Astrofisica de Andalucia), and with the support of ESA (European Space Agency) and CNES (French Space Agency). GCM outputs are compiled to build a Mars Climate Database, a freely available tool useful for the scientific and engineering communities. The Mars Climate Database (MCD) has over the years been distributed to more than 350 teams around the world. The latest series of reference simulations have been compiled in version 5.3 of the MCD which was released in 2017.To summarize, MCD v5.3 provides:- Climatologies over a series of synthetic dust scenarios: standard (climatology) year, cold (ie: low dust), warm (ie: dusty atmosphere) and dust storm, all topped by various cases of Extreme UV solar inputs (low, mean or maximum). These scenarios have been derived from home-made, instrument-derived (TES, THEMIS, MCS, MERs), dust climatology of the last 8 Martian years. The MCD also provides simulation outputs (MY24-33) representative of these actual years.- 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 columns, concentrations of many species: [CO], [O2], [O], [N2], [H2], [O3],...- A high resolution mode which combines high resolution (32 pixel/degree) MOLA topography records and Viking Lander 1 pressure records with raw lower resolution GCM results to yield, within the restriction of the procedure, high resolution values of atmospheric variables.- The possibility to reconstruct realistic conditions by combining the provided climatology with additional large scale and small scale perturbations schemes.At EGU, we will report on the latest improvements in the Mars Climate Database, with comparisons with available measurements from orbit (e.g.: TES, MCS, TGO) and landers (Viking, Phoenix, Curiosity). [ABSTRACT FROM AUTHOR]

Highlights • We examine the record of atmospheric pressure in Gale crater measured in-situ by the REMS and compare the data with pressure predictions from the Mars Climate Database (MCD). • Seasonal and daily trends in pressure data from REMS are well reproduced by MCD. • Differences between the MCD pressure data and the REMS measurements are produced by meteorological features that are identified on particular groups of sols. • We show that regional dust storms and dust abundance at the crater are important factors in the behaviour of the pressure causing most of the largest REMS-MCD differences. Abstract We examine the record of atmospheric pressure in Gale crater measured in-situ by the Rover Environmental Monitoring Station (REMS) instrument (Gómez-Elvira et al., 2012) on the Mars Science Laboratory (MSL) rover over two Martian years. We compare the data with pressure predictions from the Mars Climate Database (MCD) (Forget et al., 1999; Millour et al., 2015) version 5.2, which is a climatological database derived from numerical simulations of the Martian atmosphere produced by a General Circulation Model run over several Martian years. Seasonal and daily trends in pressure data from REMS are well reproduced by the standard climatology of the MCD using its high resolution mode. This high-resolution mode extrapolates pressure values from the nominal model into the altitude of each location using a high-resolution topography model and a fine tuning of the vertical scale height that was chosen to mimic effects of slope winds not directly accounted for in the General Circulation Model on which the MCD is based. Differences between the synthetic MCD pressure data and the REMS measurements are produced by meteorological features that are identified on particular groups of sols and quantified in intensity. We show that regional dust storms outside Gale crater and dust abundance at the crater are important factors in the behaviour of the pressure exciting larger amplitudes on the daily pressure variations and causing most of the largest REMS-MCD differences. We compare the pressure signals with published data of the dust optical depth obtained by the REMS ultraviolet photodiodes and the Mastcam instrument on MSL, and with orbital images of the planet acquired by the MARCI instrument on the Mars Reconnaissance Orbiter (MRO). We show that in some cases regional dust storms induce a characteristic signature in the surface pressure measured by REMS several sols before the dust arrives to Gale crater. We explore the capability of daily pressure measurements to serve as a fast detector of the development of dust storms in the context of the MSL, Insight and Mars 2020 missions. [ABSTRACT FROM AUTHOR]

The InSight spacecraft landed in the flat regions of Elysium Planitia on November 26th 2018. The instruments on board InSight make it capable of acting as a meteorological station at the surface of Mars. A pressure sensor (PS), two temperature and wind sensor booms (TWINS), along with the InSight FluxGate (IFG) magnetometer, form the Auxiliary Sensor Payload Suite (APSS). This is complemented by capabilities to measure surface brightness temperature by the radiometer in the Heat-Flow and Physical Properties Package (HP3) suite, to explore the impact of atmospheric processes on seismic measurements by SEIS, and to use InSight cameras to estimate atmospheric opacity (notably caused by suspended dust particles) and other atmospheric phenomena such as clouds and dust devils. We will discuss results drawn from atmospheric measurements on board InSight over the first two months of operation, highlighting new perspectives permitted by the high-frequency, continuous nature of the InSight acquisitions. Surface pressure measurements record global-to-local atmospheric phenomena: CO2 condensation (annual), dust cycle and storms (seasonal), baroclinic waves (weekly), thermal tides (daily), gravity waves (thousands of seconds), convective cells (hundreds of seconds), convective vortices (tens of seconds, leading to dust devils if dust particles are transported in the vortex). Two main large-scale wind regimes were expected from Global Climate Modeling at the InSight landing site during a typical year: towards the northwest in northern spring and summer, then in the opposite direction in southern summer. Existing in-situ measurements on Mars and Large-Eddy Simulations indicate that daytime convective vortices and cells not only impact pressure, but also temperature and winds; the nighttime atmosphere on Mars is comparatively much less turbulent and dominated by shear-driven turbulence, in contrast to the buoyancy-driven turbulence active in daytime. All such existing measurements and model predictions will be compared and challenged with InSight measurements. Seismic signatures associated with atmospheric phenomena will also be discussed, with a particular emphasis on the knowledge gained by the unprecedented measurements performed by InSight's seismometers. [ABSTRACT FROM AUTHOR]