Marek Slipski

Martian dust storms are valuable to study both for atmospheric science and for characterizing risks for future exploration missions. While dust plays an outsized role in the atmospheric of Mars, we lack a firm characterization of how dust storms initiate, grow, dissipate, and perturb the atmosphere over their lifecycles. Small (local) dust storms on Mars are particularly difficult to study; hundreds to thousands occur each Mars year, but their limited spatial extent and lifetime means we have relatively little to no atmospheric observations for each event. To investigate these local storms, we identified atmospheric measurements from the Mars Climate Sounder that coincide with recently mapped small storm boundaries from Mars Color Imager observations spanning Mars years 28-34 during the northern spring and summer. Using data science techniques to identify and aggregate these coincident observations, we extracted dust and temperature changes aligned with dust storm initiation across ~1350 events. Generally, we found that atmospheric perturbations are strong but short lived in the south, while northern local dust storms are weak. Our findings provide new insights into the atmospheric changes within small dust storms, which can inform future modeling studies and mission planning for exploring Mars.

JOINT OBSERVATIONS OF MESOSPHERIC AEROSOLS ON MARS FROM MAVEN/IUVS AND MRO/MCS Ashwin S. Braude1, Marek Slipski1, Sumedha Gupta2, Nicholas M. Schneider2, Armin Kleinböhl1, Franck Montmessin3, Sonal Jain2, Roger V. Yelle4 and Justin Deighan2 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA (ashwin.s.braude@jpl.nasa.gov) 2Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, CO, USA 3Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, Paris, France 4Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA Introduction: Aerosols in the Martian mesosphere (40 – 100 km altitude), consisting of dust, water ice and CO2 ice, act as tracers of both the water cycle and atmospheric dynamics [1,2,3], and are generated by the complex interplay of dust lofting with local perturbations in temperature and atmospheric circulation driven by zonal planetary waves (e.g. [4,5,6,7]). Although well-studied by various instruments on board Mars Express (e.g. [8,9,10,11]) and the ExoMars Trace Gas Orbiter (e.g. [12,13,14,15]), these instruments are unable to simultaneously probe the zonal and vertical structure of these layers for a given season and local time. This makes it difficult to distinguish mesospheric aerosol features driven by transient atmospheric instabilities from more persistent and predictable climatological phenomena. Since 2015, the Mars Atmosphere and Volatile EvolutioN (MAVEN) probe’s Imaging UltraViolet Spectrometer (IUVS) has conducted multiple targeted stellar occultations in close geographical and temporal proximity to limb observations made by the Mars Climate Sounder (MCS) instrument onboard the Mars Reconnaissance Orbiter (MRO). In this talk, we will present a climatology of these joint observations, identifying a) to what extent we detect mesospheric aerosol features that are consistent across both datasets and b) the lifetimes of these features. Our results will then be used to identify regional climatologies in aerosol features that can be distinguished from aerosol features generated by transient weather events.Data: MCS joint observations began in March of 2015 and continued through January of 2022, corresponding to ~40 campaigns that targeted at least 1 IUVS occultation set each. We have available 140 MCS profiles that occurred within 60 minutes, and are within 10° of latitude, 15° of longitude, and 30 minutes of local time, of a single IUVS occultation.IUVS and MCS are both sensitive to the vertical structure of both aerosols and temperature, while the longitudinal sampling of these observations at fixed latitudes and local times allows for zonal variations in aerosol structure to be extracted. From IUVS stellar occultation measurements [16], we can retrieve vertical profiles of two independent quantities: aerosol opacity up to ~110 km altitude, and an ’Ångström coefficient’ [8,17] loosely correlated with particle size (with non-zero values indicating a submicron particle population). However, aerosol particle composition is difficult to determine with great accuracy. Conversely, MCS limb observations can easily distinguish vertical profiles of dust and water ice (in units of extinction coefficient, km-1), but have little sensitivity to particle size or to aerosol opacity above approximately 60 km altitude. These measurements therefore complement each other.Preliminary Results: Detections of detached aerosol layers below 60 km in IUVS data generally map well onto water ice cloud layers in joint MCS observations, with large densities of joint water ice cloud detections at equatorial and northern latitudes during the dusty season. Conversely, aerosol features at the lowest altitudes to which IUVS is sensitive mostly correlate with increases in dust opacity detected by MCS. The main exception is during winter and early spring at southern high latitudes, where detached aerosol layers are often retrieved by IUVS at approximately 50 km altitude but entirely absent from corresponding MCS data (with an example shown in Figure 1), even though they should be easily resolvable by both datasets.Figure 1: Aerosol opacity and Ångström coefficient profiles retrieved from IUVS stellar occultations compared with dust and water ice extinction profiles retrieved from the closest three MCS observations. (top) in this observation, obtained in Southern winter at 63S latitude, IUVS observes a detached aerosol layer centred around 45 km altitude for which MCS failed to detect either a dust or a water ice layer, (bottom) in this observation, obtained in the northern tropics close to the autumn equinox, two detached layers are observed by IUVS at 40 km and 52 km altitude that are clearly determined to be water ice clouds by MCS.As with [8,18] we also often observe regions of Ångström coefficient greater than 0 directly above either the level of detectable dust in MCS observations or just above water ice cloud layers, indicating layers of smaller aerosol particles – most likely dust - located just above the haze-tops and water ice clouds detected by MCS, and often undetected by MCS. However, we find as with [11] that this pattern is neither consistent nor usually correlated with the presence or absence of water ice clouds, and appears to be highly longitude-dependent. Acknowledgments: This work was carried out at the Jet Propulsion Laboratory California Institute of Technology under a contract with NASA. We recognize support for this project from NASA grant 23-MDAP23-0060. References: [1] Bony et al. (2015), Nat. Geosci., 8, 261–268. [2] Guzewich et al. (2016), Icarus, 278, 100–118. [3] Gronoff et al. (2020), J. Geophys. Res. Space Phys., 125, e27639. [4] Banfield et al. (2000), J. Geophys. Res., 105, 9521–9538. [5] Banfield et al. (2003),...

Mesospheric CO₂‐ice clouds form in one of the coldest regions of Mars's atmosphere, but to date links between the broader thermal structure, dynamical phenomena, and the global and seasonal structure of mesospheric clouds have been tentative due to a limited sample of cloud observations. Combining a comprehensive set of cloud identifications and temperature observations from the Mars Climate Sounder onboard the Mars Reconnaissance Orbiter, we demonstrate for the first time that the spatial distribution and seasonal evolution—including the well‐known yet unexplained solstitial pause—of the aphelion mesospheric cloud population are governed by the interplay of thermal tides and gravity waves. In addition, we present the first investigation of the nighttime cloud distribution and our approach successfully explains the observed day‐to‐night differences. The significant day‐to‐night variability in observed cloud occurrence rates and likelihoods of subcondensation temperatures point toward larger nighttime particle sizes possibly due to more favorable growth conditions.

The turbopause and homopause represent the transition from strong turbulence and mixing in the middle atmosphere to a molecular‐diffusion‐dominated region in the upper atmosphere. We use neutral densities measured by the Neutral Gas and Ion Mass Spectrometer on the Mars Atmospheric and Volatile EvolutioN spacecraft from February 2015 to October 2016 to investigate the temperature structure and fluctuations of the Martian upper atmosphere. We compare those with temperature measurements of the lower atmosphere from the Mars Reconnaissance Orbiter's Mars Climate Sounder. At the lowest Mars Atmospheric and Volatile EvolutioN altitudes we often observe a statically stable region where waves propagate freely. In contrast, regions from about 20 km up to at least 70 km are reduced in stability where waves are expected to dissipate readily due to breaking/saturation. We derive homopause altitudes from Neutral Gas and Ion Mass Spectrometer N₂ and Ar densities and find that it varies between 60 and 140 km. From the standard deviations in monthly averaged temperature profiles, we determine the wave turbopause altitude where applicable and find that these altitudes agree with the homopause altitudes. We show that the homopause variability is driven by order of magnitude changes in CO₂ densities, which drastically affect the altitude at which the eddy diffusion is equal to the molecular diffusion. These variations are observed as a function of local time, latitude, and season. That the turbopause/homopause does not track a fixed density level means that the eddy diffusion coefficient at the turbopause can vary significantly, suggesting differences in the dominant breaking waves and tidal modes.

The history of Mars’ atmosphere is important for understanding the geological evolution and potential habitability of the planet. We determine the amount of gas lost to space through time using measurements of the upper-atmospheric structure made by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. We derive the structure of ³⁸Ar/³⁶Ar between the homopause and exobase altitudes. Fractionation of argon occurs as a result of loss of gas to space by pickup-ion sputtering, which preferentially removes the lighter atom. The measurements require that 66% of the atmospheric argon has been lost to space. Thus, a large fraction of Mars’ atmospheric gas has been lost to space, contributing to the transition in climate from an early, warm, wet environment to today’s cold, dry atmosphere.