Limb sounding of thermal emission in the infrared wavelength range is a powerful technique for measuring temperature and aerosols in the martian atmosphere. However, the long optical path may provide challenges to limb retrievals in high aerosol conditions. These can be mitigated by considering limb measurements in the far infrared, where opacities of most aerosols are lower than in the mid-infrared. We present analyses of radiative properties of Mars dust and water ice aerosols at far infrared wavelengths based on measurements by the Mars Climate Sounder (MCS) in limb geometry at mid- and far infrared wavelengths. For dust aerosols, derived far infrared radiative properties show a homogeneous behavior that is consistent with particle sizes in the order of 1 mu m effective radius. Far infrared radiative properties for water ice aerosols exhibit a larger variability in local time and region, leading to significant differences between the aphelion cloud belt and the north polar hood, with the resulting parameters suggesting particle sizes around 3 mu m or larger. Using the derived parameters, we develop a method for retrieving aerosol profiles from MCS limb measurements that combines information from mid- and far infrared spectroscopic channels. The use of far infrared channels enables aerosol profile retrievals from limb measurements that typically reach about a scale height deeper into the atmosphere than would be possible using mid-infrared channels only. The extended vertical range of the aerosol profiles allows the derivation of aerosol column optical depths through vertical integration, with dust column derivations in global or large-scale regional dust storms also being available by extrapolating dust profiles below the lowest retrievable altitude of a limb measurement. The quantification of aerosol columns allows us to retrieve surface brightness temperatures from MCS on-planet viewing measurements that are corrected for atmospheric contributions. We show that differences between surface brightness and top-of-the-atmosphere temperatures are typically within 20 K, with surface brightness temperatures generally being warmer (colder) than top-of-the-atmosphere temperatures at daytime (nighttime), except at high latitudes.

NASA’s Perseverance rover’s Mars Environmental Dynamics Analyzer is collecting data at Jezero crater, characterizing the physical processes in the lowest layer of the Martian atmosphere. Here we present measurements from the instrument’s first 250 sols of operation, revealing a spatially and temporally variable meteorology at Jezero. We find that temperature measurements at four heights capture the response of the atmospheric surface layer to multiple phenomena. We observe the transition from a stable night-time thermal inversion to a daytime, highly turbulent convective regime, with large vertical thermal gradients. Measurement of multiple daily optical depths suggests aerosol concentrations are higher in the morning than in the afternoon. Measured wind patterns are driven mainly by local topography, with a small contribution from regional winds. Daily and seasonal variability of relative humidity shows a complex hydrologic cycle. These observations suggest that changes in some local surface properties, such as surface albedo and thermal inertia, play an influential role. On a larger scale, surface pressure measurements show typical signatures of gravity waves and baroclinic eddies in a part of the seasonal cycle previously characterized as low wave activity. These observations, both combined and simultaneous, unveil the diversity of processes driving change on today’s Martian surface at Jezero crater.

A vigorous regional dust storm substantially altered both the global atmospheric thermal structure and the magnitude and spatial distribution of dust loading within the Mars atmosphere between 1 and 9 June 2018. We examine the development and decay of this storm in latitude, longitude, altitude, and time, employing observations by the Mars Climate Sounder on board the Mars Reconnaissance Orbiter. Dust layer top altitudes rose from seasonal-normal values of similar to 40 to similar to 70 km. Dust lofting to high altitudes was localized between 0 degrees and similar to 60 degrees W longitude, and between 60 degrees N and 60 degrees S latitude. Intensification of paired meridional overturning circulation cells within the study area is confirmed by strong nighttime dynamical heating in higher latitudes of both hemispheres. By the end of this episode, significant dust loading was present at altitudes greater than 50 km above all longitudes on Mars, and other dust lifting centers had been activated.

The largest of dust storms on Mars are global dust events (GDEs) that affect essentially every aspect of the Martian atmosphere but do not occur in every Mars year. The Mars Climate Sounder globally observed the most recent GDE in 2018 throughout its lifecycle. The event started shortly after the southern spring equinox, with the first Mars Climate Sounder signature detected on 2 June 2018 (Ls = 186.2°). It grew into a mature global event by the end of June (Ls ~ 198°), with drastic changes to the atmospheric temperature, dust, and water ice profiles. It decayed over several months, reaching background conditions around southern summer solstice in October 2018. The 2018 GDE was very similar to the 2001 event, including the seasonal development and temperatures. GDEs appear to be distinct from even the largest regional dust storms. GDEs have 50‐Pa zonal tropical temperatures >220 K while no regional dust storm exceeds 205 K.

The stability of the residual carbon dioxide cap near the south pole of Mars is currently not well understood. The cap's survival depends on its radiation budget, controlled by the visible albedo and infrared emissivity. We investigated the role of CO2 snowfall in altering the albedo and emissivity, leading to the observed asymmetry in the net CO2 accumulation at the two poles. Uncontaminated snowfall increases albedo, and lowers emissivity, due to scattering by optically thick clouds and granular surface deposits. Data from the Mars Climate Sounder (MCS) show that fall and winter snowfall is correlated with higher springtime albedo at both poles. For the seasonal CO2 deposits in each polar region >60° latitude, we find mean albedo values of 0.39 in the north and 0.51 in the south, and winter 32‐μm emissivity values of 0.84 in the north and 0.87 in the south. Using a radiative transfer model and the MCS data, we find that the north polar deposits have ∼10× higher dust content than those in the south, explaining the ∼31% lower albedo of the north seasonal cap during spring. Our model shows that greater amounts of snowfall can explain the ∼4% lower emissivity of the north polar seasonal cap. These findings demonstrate that winter snowfall and dust transport affect the composition of Mars' seasonal ice caps and polar energy balance. Snowfall and dust loading are therefore important in modeling the CO2 cycle on Mars, as well as the planet's long‐term climate variations.

The impact of gravity waves (GW) on diurnal tides and the global circulation in the middle/upper atmosphere of Mars is investigated using a General Circulation Model (GCM). We have implemented a stochastic parameterization of non-orographic GW into the Laboratoire de M\'et\'eorologie Dynamique (LMD) Mars GCM (LMD-MGCM) following an innovative approach. The source is assumed to be located above typical convective cells ($\sim$ 250 Pa) and the effect of GW on the circulation and predicted thermal structure above 1 Pa ($\sim$ 50 km) is analyzed. We focus on the comparison between model simulations and observations by the Mars Climate Sounder (MCS) on board Mars Reconnaissance Orbiter during Martian Year 29. MCS data provide the only systematic measurements of the Martian mesosphere up to 80 km to date. The primary effect of GW is to damp the thermal tides by reducing the diurnal oscillation of the meridional and zonal winds. The GW drag reaches magnitudes of the order of 1 m/s/sol above 10$^{-2}$ Pa in the northern hemisphere winter solstice and produces major changes in the zonal wind field (from tens to hundreds of m/s), while the impact on the temperature field is relatively moderate (10-20K). It suggests that GW induced alteration of the meridional flow is the main responsible for the simulated temperature variation. The results also show that with the GW scheme included, the maximum day-night temperature difference due to the diurnal tide is around 10K, and the peak of the tide is shifted toward lower altitudes, in better agreement with MCS observations.

INITIAL GROWTH PHASE OF THE PLANET-ENCIRCLING DUST EVENT OF 2018. J. H. Shirley , A. Kleinbӧhl, D. M. Kass, N. G. Heavens, J. T. Schofield, D. T. McCleese, L. J. Steele, S. Piqueux, and the MRO-MCS Science Team. JPL-California Institute of Technology, 4800 Oak Grove Dr., Pasadena CA 91109 USA. Space Science Institute, Boulder, CO USA. Retired, Pasadena, CA, USA, Synoptic Sciences, Pasadena, CA, USA. (James.H.Shirley@jpl.nasa.gov)

Introduction: The yearly waning and waxing of the seasonal polar caps represents one of the most dramatic expression of the CO2 cycle on Mars, with massive amounts of carbon dioxide cyclically exchanged between the atmosphere and the surface [1]. As CO2 condenses on the surface in the local Fall and Winter, non-condensable species remain and accumulate in the atmospheric column, resulting in a decrease of the CO2 partial pressure and thus a lowering of the CO2 frost point temperature TCO2 [2]. We determine the lowering of TCO2, and discuss its impact on the polar energy budget and regional circulation. Methods: To determine TCO2, we bin Mars Climate Sounder (MCS) on Mars Reconnaissance Orbiter [3] retrieved surface temperatures acquired near 22 (T22) and 12 μm (T12) over the Polar Regions (10° in latitude and 10° Ls). In order to obtain kinetic surface temperatures, we perform a necessary emissivity correction [4] because CO2 ice emissivity depends strongly on crytal size. The emissivity correction relies on the unique spectral properties of CO2 ice at 12 and 22 μm (Fig. 1), resulting in a quasi linear relationship between T12 and T12 – T22 (see [4], and Fig. 2). When T12 = T22 (intercept of the regression line), the surface emissivity must approach 1, and the brightness temperature equals the kinetic temperature TCO2.

MARS WEATHER AND CLIMATE: AN ORBITAL CONSTELLATION FOR ATMOSPHERIC PROFILING AND SURFACE THERMOPHYSICS A. Kleinböhl, J. T. Schofield, D. M. Kass, S. Piqueux, D. J. McCleese, A. Spiga, S. J. Greybush, T. Navarro Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA; Synoptic Science, Altadena, CA; Sorbonne University, Paris, France; PennState, University Park, PA; University of California, Los Angeles, CA. (Armin.Kleinboehl@jpl.nasa.gov)

Introduction: A significant fraction of the Martian atmosphere condenses on the surface in the polar regions during the local Fall and Winter. As a result, the volumic mixing ratio of non-condensable gases, i.e. Ar (~1.9%), N2 (~1.9%), O2 (~0.1%), and CO (~0.1%) [1] is expected to increase as a function of season and latitude [2,3,4,19]. Observations have confirmed this depletion [5,6], at least in the South. The low brightness temperatures of CO2 ice noticed in places may also be an expression of noncondensable gas enrichment near the surface [7,8,9]. As the non-condensable gases are enriched, the partial pressure of CO2 decreases. The decrease in partial pressure results in a decrease in equilibrium condensation temperature for the surface frosts. Here, we present an analysis of North and South CO2 seasonal caps surface temperature observations by the Mars Climate Sounder (MCS) [10,11] onboard the Mars Reconnaissance Orbiter. In the South, we show that ground temperatures associated with frozen surfaces are ~0-4 K lower than anticipated, with latitudinal and seasonal trends generally in phase with the growth and retreat of the seasonal polar cap. Near-surface non-condensable gas mixing ratios implied by these low measurements approaches ~50%, close to modeled values [2,3,4,19], but larger than measured for the entire atmospheric column (e.g., ~20% [5,6]). In the North, a deep depletion is observed near the pole (0-5K, equivalent to <50% CO2), but with a transient increase near the peak of the polar night (near Ls~270).

AbstractWe find that during the dusty season on Mars (southern spring and summer) of years without a global dust storm there are three large regional‐scale dust storms. The storms are labeled A, B, and C in seasonal order. This classification is based on examining the zonal mean 50 Pa (∼25 km) daytime temperature retrievals from TES/MGS and MCS/MRO over 6 Mars Years. Regional‐scale storms are defined as events where the temperature exceeds 200 K. Examining the MCS dust field at 50 Pa indicates that warming in the Southern Hemisphere is dominated by direct heating, while northern high latitude warming is a dynamical response. A storms are springtime planet encircling Southern Hemisphere events. B storms are southern polar events that begin near perihelion and last through the solstice. C storms are southern summertime events starting well after the end of the B storm. C storms show the most interannual variability.

Introduction: Recent advances in algorithms used to process data from the Mars Climate Sounder (MCS) [1] permit the study of the Mars polar atmosphere with unprecedented spatial and temporal resolution and coverage. We have used this improved observational record in comparisons with General Circulation Models (GCM) and reanalysis. To date, limitations in the observations have made more difficult studies of the strengths and weaknesses in simulations of the Martian polar atmosphere, such as the polar vortices. No less important are recent advances in reanalysis applied to MCS data, which has the potential for improving understanding by producing high-fidelity simulations of atmospheric fields not directly observed or retrieved and at spatial and temporal resolutions not available to existing measurement techniques.

Introduction: Limb sounding of thermal emission in the infrared wavelength range is a powerful technique for measuring dust and water ice aerosols in the martian atmosphere. It provides vertical profile information and, due to the long optical path, typically has a higher sensitivity compared with nadir viewing measurements. However, the limb path might become opaque in high aerosol conditions, preventing a limb sounding measurement from penetrating the atmosphere. While atmospheric opacities of aerosols in the far infrared are typically lower than in the midinfrared, the spectroscopic parameters that control aerosol absorption in the far-infrared are often not well quantified. Here we use limb measurements and atmospheric profile retrievals by the Mars Climate Sounder (MCS) to evaluate aerosol spectroscopic parameters in the far infrared. We derive empirical extinction efficiencies for dust and water ice around 32 μm and 42 μm, respectively. These far infrared extinction efficiencies will enable MCS limb retrievals of aerosol profiles in atmospheric conditions where midinfrared retrievals are challenging, e.g. in dust storms or the aphelion cloud belt. We demonstrate that using the 32 μm channel of MCS for dust retrievals extends the retrievable altitude range in dust storm conditions by about a scale height.

High altitude clouds have been observed in the Martian atmosphere. However, their properties still remain to be characterized. Mars Climate Sounder (MCS) aboard Mars Reconnaissance Orbiter (MRO) is an instrument that measures radiances in the thermal infrared, both in limb and nadir views. It allows us to retrieve vertical profiles of radiance, temperature and aerosols. Using the MCS data and radiative transfer model coupled with an automated inversion routine, we can investigate the chemical composition of the high altitude clouds. We will present the first results on the properties of the clouds. CO2 ice is the best candidate to be the main component of some high altitude clouds due to the most similar spectral variation compared to water ice or dust, in agreement with previous studies. Using cloud composition of contaminated CO2 ice (dust core surrounded by CO2 ice) might improve the fitting result, but further study is needed.

Introduction: The complex structure and seasonal evolution of the Mars polar vortices continue to present challenges to General Circulation Models (GCM) [1]. To date, limitations in the observational record are central to the difficulty in modeling these prominent features of the Martian atmosphere. A new 2D retrieval scheme has been applied to data from the Mars Climate Sounder (MCS) revealing details of the north and south polar vortices not previously available. Observations now include high resolution maps of temperature and aerosols of dust and H2O ice. In addition, CO2 ice aerosol can be studied in the polar region. Comparisons of MCS data and GCM output of the thermal structure and aerosol distributions in the vortices are presented in this paper.

EMCS: The Exomars Climate Sounder (EMCS) investigation Conference or Workshop Item How to cite: Schofield, J. T.; Kass, D. M.; Kleinbhl, A.; McCleese, D. J.; Allen, M. A.; Foote, M. C.; Jeganathan, M.; Forget, F.; Spiga, A.; Talagrand, O.; Lefe, F.; Mtn, A.; Fouchet, T.; Bowles, N.; Calcutt, S. B.; Irwin, P. G. J.; Read, P. L.; Lewis, S. R.; Barnes, J. R.; Bougher, S. W. and Haberle, R. M. (2011). EMCS: The Exomars Climate Sounder (EMCS) investigation. In: Fourth International Workshop: Mars Atmosphere Modelling and Observations, 8-11 Feb 2011, Paris, France.

Introduction: Martian northern spring and summer (Ls 0° to 180°) are quite different from southern spring and summer (Ls 180° to 360°) [1]. The former are cool, relatively dust free with extensive water vapor and ice clouds. The latter are warm and dusty with the regular occurrence of very large dust storms. These seasonal differences are true in both hemispheres. The northern spring and summer are also referred to as the aphelion season [2,3] since aphelion (Ls 71°) occurs near the northern solstice (Ls 90°) and the reduced insolation due to the increased distance to the sun is a primary driver of the overall cooler seasonal climate. The low temperatures lead to an increase in equatorial water ice clouds, called the aphelion cloud belt [4]. The aphelion season is also recognized for its low inter-annual variability [4,5,6], especially in a climatological sense. There is still weather and dust storm activity during the season, especially in the mid-latitudes and polar regions [7].