Abstract. As of the early 2000s, multiple contemporaneous global and vertically resolved nitrous oxide (N2O) datasets have become available from a suite of limb-viewing satellite instruments. Together, these datasets provide a 23-year and counting continuous N2O record. Due to its long lifetime, N2O is a valuable tracer of atmospheric transport, and a reliable long-term record therefore allows the examination of changes in stratospheric circulation as a result of climate change. In order to combine results from different satellite datasets for these purposes, it is necessary to account for their biases, which can be determined through evaluation studies. Here, N2O measurements in the upper troposphere and lower-to-middle stratosphere (5–40 km) are evaluated from five different satellite limb sounders: ACE-FTS on SCISAT, HIRDLS and MLS on Aura, MIPAS on Envisat, and SMR on Odin. This is done by comparing colocated satellite measurements with each other to determine the instruments’ relative biases and by comparing each dataset with independent reference data from balloon-borne instruments. ACE-FTS (v5.2), the two MIPAS datasets (V8), and SMR (v3.0.0) agree within ±5–10 %, but HIRDLS (v07) has variable performance depending on the region and time of year. MLS (v5) has a persistent deviation resulting in a low bias of up to 30 % in the lower stratosphere at 24 km. This bias is substantially reduced in v6. These findings are corroborated by the comparisons of each satellite instrument with balloon-borne data. This study lays the groundwork for creating a merged and bias-corrected N2O time series spanning from 2002 to the present using ACE-FTS, MIPAS, SMR, and possibly the MLS v6 dataset.

Introduction: We have currently accumulated over 25 years of continuous satellite data on Martian dust and, generally, on the weather of the Red Planet. By utilizing data from instruments operating in the thermal infrared such as the Thermal Emission Spectrometer (TES, onboard the Mars Global Surveyor satellite), Thermal Emission Imaging System (THEMIS, onboard Mars Odyssey), and Mars Climate Sounder (MCS, onboard the Mars Reconnaissance Orbiter), we have been able to reconstruct diurnal maps of column dust optical depth (CDOD) spanning more than 13 Martian years (MY) from 1999 to the present day [1, 2, 3, 4, 5]. Two types of maps exist: ‘gridded maps’ (the mesh is regular but values are missing where there are no observations) and ‘kriged maps’ (interpolated from the gridded maps using kriging to produce complete maps). These longitude-latitude maps are used as 'dust scenario' in the Mars Climate Database [6], among many other applications. They are routinely updated and made publicly available in NetCDF or FITS formats (see the links to the datasets in the acknowledgments section).Recent developments: The daily CDOD maps covering MY 24 through part of MY 27 have been recently improved by using revised retrievals of column dust optical depths from TES observations (refer to the link in the acknowledgments section for accessing this updated dataset). The top four panels of Figure 1 (MY 24, 25, 26, 27) show zonal means of these improved CDOD maps normalized to 610 Pa (MY 27 zonal mean is actually a combination of revised TES-based maps and previous THEMIS-based maps).The arrival of the Emirates Mars Mission (EMM) 'Hope' spacecraft in a low-inclination, high-altitude orbit around Mars has enabled simultaneous monitoring of the full disk of the Martian atmosphere. The CDOD retrievals from the Emirates Mars InfraRed Spectrometer (EMIRS) observations significantly enhance the quality of our dust maps, enabling for the first time quasi-continuous monitoring of storms over multiple local times [7]. The bottom two panels of Figure 1 show zonal means of, respectively, MCS-based maps and EMIRS-based maps for MY 36. Work is in progress to 1) understand the differences, and 2) integrate CDOD information from both MCS and EMIRS to produce combined daily maps.Moreover, the availability of visible images from the EMM/Emirates Exploration Imager (EXI) on one side [8], and retrievals of CDOD in the visible from TES Emission Phase Function (EPF) observations on the other (refer to the link in the acknowledgments section for access to this novel dataset), enables cross-comparison and validation of the daily gridded dust maps with an unprecedented level of detail.Figure 1: Zonal means of CDOD normalized to 610 Pa for 13 Martian years. The top four panels (MY 24, 25, 26, 27) show zonal means of improved maps using revised TES retrievals. The bottom two panels show zonal means of, respectively, MCS-based maps and EMIRS-based maps for MY 36.Tracking of dust events: From the daily CDOD maps, it is possible to identify large-scale dust events (“storms”) reaching regional and planetary scales, follow their evolution, and create statistics of their main characteristics such as trajectory, area, and optical depth (see an example in Figures 2 to 5). A new development in progress is the identification and tracking of large-scale dust events using unsupervised machine learning algorithms [9].A key outcome of this work is the production of a catalog of historic large-scale dust events, which can be routinely updated with new events as new dust maps become available. An important aspect of creating a catalog of dust events is the precise determination of their occurring time. While a Mars calendar based on solar longitude works for many applications, it does not work well for daily maps produced at a discrete number of sols per year. Therefore, we choose to use a sol-based calendar as described in [1, Appendix A]. Each Martian year has either 669 or 668 sols, following a 5-year cycle. The beginning and end of a year is always at midnight at the prime meridian, hence a new year in our sol-based calendar does not necessarily start at LS=0° (see Figure 6).Figure 2: Sol-by-sol identification and tracking of the evolution of a dust sequence (“storm”) in MY 36 between LS=309° and LS=318° from daily EMIRS-based CDOD maps normalized to 610 Pa. The rest of the daily maps is visible in the transparent background.Figure 3: Plot of the trajectory of the centroid of the dust event shown in Figure 2. Figure 4: Plot of the time evolution of the area of the dust event shown in Figure 2.Figure 5: Plot of the time evolution of the average and 1-σ envelope of the CDOD normalized to 610 Pa for the dust event shown in Figure 2.Figure 6: This table shows the Earth UTC dates and Mars solar longitudes of the beginning of Martian years 1 through 38 in our sol-based calendar (see also [1]).Acknowledgments: LM acknowledges support from CNES and ESA MCD project. BKG was supported by UAE University Grant G00003407. Work at the Jet Propulsion Laboratory, California Institute of Technology, is supported by NASA.The multi-annual dataset of daily gridded and kriged maps v2.x for MY24 through MY36 is available on the MCD webpage (NetCDF format) at https://www-mars.lmd.jussieu.fr/mars/dust_climatology/ and on the VESPA repository (FITS format) at https://bit.ly/3QMFfIf (shortened link)The latest v3.0 of the daily gridded maps for MY24 through part of MY27, together with corresponding TES CDOD retrievals in the infrared and in the visible, are available on the NASA PDS (atmosphere node) at:https://atmos.nmsu.edu/data_and_services/atmospheres_data/MARS/montabone.htmlReferences:[1] L. Montabone et al., 2015, doi: 10.1016/j.icarus.2014.12.034.[2] L. Montabone et al., 2020, doi: 10.1029/2019JE006111.[3] M. D. Smith, 2009, doi: [10.1016/j.icarus.2009.03.027[4] M. D. Smith, 2004, doi: 10.1016/j.icarus.2003.09.010[5] A. Kleinboehl et al., 2009, doi: 10.1029/2009JE003358[6] E. Millour et al., EPSC2022-786, https://doi.org/10.5194/epsc2022-786, 2022.[7] Smith et al, 2022, doi : 10.1029/2022GL099636[8] B. K. Guha et al., 2023, doi: 10.1029/2023JE008156[9] T. Lombard & L. Montabone, 10th International Conference on Mars, 2024

Montabone et al., 2015 and 2020, [1, 2] have developed an iterative, weighted, running mean methodology to grid the available retrievals of atmospheric column dust optical depth (CDOD) from multi-annual and multi-instrument spacecraft observations at Mars. The application of this methodology has produced daily gridded maps of CDOD from Martian Year (MY) 24 through 35, using Mars Global Surveyor/Thermal Emission Spectrometer and Mars Odyssey/Thermal Emission Imaging System nadir observations, as well as the estimates of this quantity from Mars Reconnaissance Orbiter/Mars Climate sounder (MRO/MCS) limb observations. Given the lack of dust observations at certain times and locations, the daily gridded maps have missing values at some grid points. Kriging spatial interpolation has been used to produce regular maps that are useful as multiannual dust scenarios for model simulations, and for the Mars Climate Database (MCD) statistics [3].We have now adapted this methodology to include CDOD retrievals from Emirates Mars Mission/Emirates Mars Infrared Spectrometer (EMM/EMIRS) nadir observations in MY 36 [4]. The specificity of EMIRS spatial and temporal coverage as well as the extended nature of its footprint are taken into account when carrying out the gridding. We will present a cross-comparison of maps obtained using only EMIRS retrievals and maps obtained using only MCS retrievals, in the attempt to understand what is the best approach to produce a MY 36 dust scenario that makes the best use of both instruments. We will particularly focus on the evolution of large-scale dust storms in MY 36.References: [1] Montabone, L., et al. (2015) Icarus 251, pp. 65-95, doi: 10.1016/j.icarus.2014.12.034 ; [2] Montabone, L., et al. (2020) J. Geophys. Res. - Planets, doi: 10.1029/2019JE006111 ; [3] http://www-mars.lmd.jussieu.fr (Publicly available dust gridded maps can be currently found up to MY 35 by clicking on the “climatologies of Martian atmospheric dust” link under “Martian dust Climatology”) ; [4] Smith, M.D., et al. (2022) Geophys. Res. Lett. 49, Issue 15, doi: 10.1029/2022GL09963

Nitrous oxide (N2O) is the fourth most important greenhouse gas in the atmosphere and is considered the most important current source gas emission for global stratospheric ozone depletion (O3). It has natural and anthropogenic sources, mainly as an unintended by-product of food production activities. This work examines the identification and quantification of trends in the N2O concentration from the middle troposphere to the middle stratosphere (MTMS) by in situ and remote sensing observations. The temporal variability of N2O is addressed using a comprehensive dataset of in situ and remote sensing N2O concentrations based on aircraft and balloon measurements in the MTMS from 1987 to 2018. We determine N2O trends in the MTMS, based on observations. This consistent dataset was also used to study the N2O seasonal cycle to investigate the relationship between abundances and its emission sources through zonal means. The results show a long-term increase in global N2O concentration in the MTMS with an average of 0.89 ± 0.07 ppb/yr in the troposphere and 0.96 ± 0.15 ppb/yr in the stratosphere, consistent with 0.80 ppb/yr derived from ground-based measurements and 0.799 ± 0.024 ppb/yr ACE-FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer) satellite measurements.

This review provides an analysis of activities undertaken by the Mars 2020 Council of Atmospheres (CoA) in support of the entry, descent, and landing (EDL) of the Mars 2020 rover Perseverance in Jezero crater, Mars. The activities of the CoA were designed to evaluate the safety of early-stage landing site candidates and, later, to constrain the range of plausible conditions expected at Jezero crater during the early northern spring season of EDL, following the successful blueprint of similar councils for prior landed Mars missions. The multiyear effort of the CoA involved using a combination of numerical modeling of the local Martian atmosphere with limited-domain mesoscale models and atmospheric reanalysis using data assimilation techniques, along with atmospheric observations from multiple orbiting assets, to generate an atmospheric “forecast” for the day of landing. Here we present an overview of these activities, focusing in greater detail on those elements that depart from prior CoA activities as performed for Mars Phoenix, Mars Science Laboratory, and the InSight lander. Following the successful landing of Perseverance on 2021 February 18, reconstruction and reassessment activities were performed and are presented here, comparing prelanding predictions with actual, as-flown conditions.

The Martian climate system has been revealed to rival the complexity of Earth’s. Over the last 20 yr, a fragmented and incomplete picture has emerged of its structure and variability; we remain largely ignorant of many of the physical processes driving matter and energy flow between and within Mars’ diverse climate domains. Mars Orbiters for Surface, Atmosphere, and Ionosphere Connections (MOSAIC) is a constellation of ten platforms focused on understanding these climate connections, with orbits and instruments tailored to observe the Martian climate system from three complementary perspectives. First, low-circular near-polar Sun-synchronous orbits (a large mothership and three smallsats spaced in local time) enable vertical profiling of wind, aerosols, water, and temperature, as well as mapping of surface and subsurface ice. Second, elliptical orbits sampling all of Mars’ plasma regions enable multipoint measurements necessary to understand mass/energy transport and ion-driven escape, also enabling, with the polar orbiters, dense radio occultation coverage. Last, longitudinally spaced areostationary orbits enable synoptic views of the lower atmosphere necessary to understand global and mesoscale dynamics, global views of the hydrogen and oxygen exospheres, and upstream measurements of space weather conditions. MOSAIC will characterize climate system variability diurnally and seasonally, on meso-, regional, and global scales, targeting the shallow subsurface all the way out to the solar wind, making many first-of-their-kind measurements. Importantly, these measurements will also prepare for human exploration and habitation of Mars by providing water resource prospecting, operational forecasting of dust and radiation hazards, and ionospheric communication/positioning disruptions.

The study of planetary atmospheres in a truly comparative manner will require a devotion of resources and a philosophy of planetary exploration that differs from the current trend.Fly-by, Orbit, Land, Sample Return does not easily mesh with a requirement for global, long-term monitoring of an atmosphere to characterize the spectrum of spatiotemporal changes that define it.Such investigations of atmospheres within NASA's Planetary Science purview will be essential for maximizing the understanding of information returned from the characterization of terrestrial exoplanets under the purview of NASA Astrophysics.The heritage of models to elucidate the required atmospheric observations draws heavily upon those already utilized in the purview of NASA Earth Sciences, and will enrich such efforts.Finally, the commissioning of multiple spacecraft, all focused on characterizing the range of drivers of planetary atmospheric evolution -the largest of which invariably is the Sun -will lead to improved understanding of the Heliospheric environment (obviously under NASA's Heliophysics purview).Hence, the establishment of an organization whose purpose is to foster such exploration of planetary atmospheres will have broad ramifications both for planetary science, as well as cross-disciplinary benefits across all four of NASA's science subdivisions.

More than 85% of the 23 investigations developed by VEXAG are largely accomplished via a NF mission centered on a variable-altitude balloon (aerobot) supported by a science/comm orbiter. Circling Venus >15 times over ~90 days, the aerobot repeatedly visits 52–62 km alts as it semi-continuously samples a host of environmental & surface parameters.

It has been established that dust in the atmosphere of Mars is not distributed homogeneously in the vertical but exhibits layering in the lower atmosphere. Recently published results also suggest a dust maximum in the middle atmosphere that predominantly occurs at 50-60 km altitude on the daytime hemisphere. We use measurements from the Mars Climate Sounder to investigate the distribution of dust above similar to 40 km altitude. Our results do not support the existence of widespread dust in the middle atmosphere of Mars inferred from earlier observations. The average dust extinction does not exceed 10(-6) km(-1) at 463 cm(-1) above 50 km altitude in atmospheric conditions without large dust storms. (C) 2015 Elsevier Inc. All rights reserved.

Near‐infrared spectra taken in a limb‐viewing geometry by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the Mars Reconnaissance Orbiter provide a useful tool for probing atmospheric structure. Specifically, the observed radiance as a function of wavelength and height above the limb enables the vertical distribution of both dust and water ice aerosols to be retrieved. More than a dozen sets of CRISM limb observations have been taken so far providing pole‐to‐pole cross sections, spanning more than a full Martian year. Radiative transfer modeling is used to model the observations taking into account multiple scattering from aerosols and the spherical geometry of the limb observations. Both dust and water ice vertical profiles often show a significant vertical structure for nearly all seasons and latitudes that is not consistent with the well‐mixed or Conrath‐ v assumptions that have often been used in the past for describing aerosol vertical profiles for retrieval and modeling purposes. Significant variations are seen in the retrieved vertical profiles of dust and water ice aerosol as a function of season. Dust typically extends to higher altitudes (~40–50 km) during the perihelion season than during the aphelion season (<20 km), and the Hellas region consistently shows more dust mixed to higher altitudes than other locations. Detached water ice clouds are common, and water ice aerosols are observed to cap the dust layer in all seasons.

We present south polar winter infrared observations from the Mars Climate Sounder (MCS) and test three hypotheses concerning the origins of “cold spots”: regions of anomalously low infrared brightness temperatures, which could be due to enrichment in non‐condensable gases, low‐emissivity surface frost, or optically thick CO2 clouds. Clouds and surface frosts have been historically difficult to distinguish, but the unique limb sounding capability of MCS reveals extensive tropospheric CO2clouds over the cold spots. We find that both clouds and surface deposits play a significant role in lowering the infrared emissivity of the seasonal ice cap, and the granular surface deposits are likely emplaced by snowfall. Surface temperatures indicate the polar winter atmosphere is enriched by a factor ∼5–7 in non‐condensable gases relative to the annual average, consistent with earlier gamma ray spectrometer observations, but not enough to account for the low brightness temperatures. A large ∼500‐km diameter cloud with visible optical depth ∼0.1–1.0 persists throughout winter over the south polar residual cap (SPRC). At latitudes 70–80°S, clouds and low emission regions are smaller and shorter‐lived, probably corresponding to large‐grained “channel 1” clouds observed by the Mars Orbiter Laser Altimeter. Snowfall over the SPRC imparts the lowest emissivity in the south polar region, which paradoxically tends to reduce net accumulation of seasonal CO2 by backscattering infrared radiation. This could be compensated by the observed anomalously high summertime albedo of the SPRC, which may be related to small grains preserved in a rapidly formed snow deposit.

The Martian polar night distribution of 1.27 μm (0–0) band emission from O2 singlet delta [O2(1Δg)] is determined from an extensive set of Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Imaging Spectral Mapping (CRISM) limb scans observed over a wide range of Mars seasons, high latitudes, local times, and longitudes between 2009 and 2011. This polar nightglow reflects meridional transport and winter polar descent of atomic oxygen produced from CO2 photodissociation. A distinct peak in 1.27 μm nightglow appears prominently over 70–90NS latitudes at 40–60 km altitudes, as retrieved for over 100 vertical profiles of O2(1Δg) 1.27 μm volume emission rates (VER). We also present the first detection of much (×80 ± 20) weaker 1.58 μm (0–1) band emission from Mars O2(1Δg). Co‐located polar night CRISM O2(1Δg) and Mars Climate Sounder (MCS) (McCleese et al., 2008) temperature profiles are compared to the same profiles as simulated by the Laboratoire de Météorologie Dynamique (LMD) general circulation/photochemical model (e.g., Lefèvre et al., 2004). Both standard and interactive aerosol LMD simulations (Madeleine et al., 2011a) underproduce CRISM O2(1Δg) total emission rates by 40%, due to inadequate transport of atomic oxygen to the winter polar emission regions. Incorporation of interactive cloud radiative forcing on the global circulation leads to distinct but insufficient improvements in modeled polar O2(1Δg) and temperatures. The observed and modeled anti‐correlations between temperatures and 1.27μm band VER reflect the temperature dependence of the rate coefficient for O2(1Δg) formation, as provided in Roble (1995).

The Mars Climate Sounder (MCS) has obtained measurements of the Martian atmosphere for one Mars year. Onboard the Mars Reconnaissance Orbiter (MRO), MCS continues to acquire high vertical resolution profiles of temperature, dust, condensates of CO2 and H2O, and water vapor by observing the limb of the atmosphere from the surface to 80 km in the spectral intervals 0.3 – 3 ?m and 11.5 – 45 ?m [1]. This paper describes the investigation and introduces some of the observations being studied by the MCS science team. Other presentations by the team at this workshop will describe in greater detail results of ongoing research using MCS data.

We analyze measurements of ClO across the terminator taken by the Airborne Submillimeter Radiometer (ASUR) in the activated vortices of the Arctic winters of 1995/1996, 1996/1997, and 1999/2000 to evaluate the plausibility of various determinations of the ClO-dimer photolysis cross section and the rate constant controlling the thermal equilibrium between ClO-dimer and ClO. We use measured ClO during sunlit conditions to estimate total active chlorine (ClOx). As the measurements suggest nearly full chlorine activation in winter 1999/2000, we compare ClOx estimates based on various photolysis frequencies of ClO-dimer with total available inorganic chlorine (Cly), estimated from an N2O-Cly correlation established by a balloon-borne MkIV interferometer measurement. Only ClO-dimer cross sections leading to the fastest photolysis frequencies in the literature (including the latest evaluation by the Jet Propulsion Laboratory) give ClOx mixing ratios that overlap with the estimated range of available Cly. Slower photolysis rates lead to ClOx values that are higher than available Cly. We use the ClOx calculated from sunlit ClO measurements to estimate ClO in darkness based on different equilibrium constants, and compare it with ASUR ClO measurements before sunrise at high solar zenith angles. Calculations with equilibrium constants published in recent evaluations of the Jet Propulsion Laboratory give good agreement with observed ClO mixing ratios. Equilibrium constants leading to a higher ClO/ClOx ratio in darkness yield ClO values that tend to exceed observed abundances. Perturbing the rates for the ClO+BrO reaction in a manner that increases OClO formation and decreases BrCl formation leads to lower ClO values calculated for twilight conditions after sunset, resulting in better agreement with ASUR measurements.