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Martian global dust storms (GDS) can significantly affect the water cycle in the lower atmosphere (0−40 km). We compare the evolution of water vapor abundances, dust opacity and surface temperatures in the Southern Polar Region (SPR) during GDS years of MY25, MY28, and MY34 relative to years without GDS. During all GDS years, the vapor abundances decrease in the lower atmosphere in the SPR following the storm. Our results suggest that this decrease could be the result of disruption of the southward transport of vapor by atmospheric circulation. Alternatively, the decrease in vapor abundances could be caused by decreased desorption of vapor from the subsurface. Plain Language Summary: This work presents comprehensive analysis of how water vapor in the Martian polar atmosphere reacts to large dust storms in different years. Measurements of water vapor, atmospheric dust, and surface temperatures collected by different spacecraft instruments in years with and without large dust storms are compared. These comparisons inform our understanding of how Martian water vapor is transported through the atmosphere and how it interacts with the surface. Large dust storms decrease the amount of water vapor in the southern polar region. This may indicate that the transport of vapor to the pole is reduced by the storms, or that dusty atmosphere cools the surface and reduces the amount of vapor released from the subsurface. Key Points: Water vapor abundances over the Southern Polar Region of Mars are reduced following a global dust storm (GDS)The decrease in water vapor abundances could be caused by disruption of southward vapor transport by a GDSAlternatively, the decrease could be caused by changes in the surface‐atmosphere vapor exchange [ABSTRACT FROM AUTHOR]

We report retrievals of atmospheric water vapor abundances in and around the South Polar Region (SPR) of Mars during spring and summer of Mars Years (MY) 24–26 (1999–2003). The retrieval utilizes infrared spectra collected by the Thermal Emission Spectrometer (TES) aboard the Mars Global Surveyor (MGS) spacecraft. Modifications to the existing retrieval algorithm enable the first retrievals of water vapor abundances over regions covered by the seasonal CO 2 frost during spring. We present polar maps of water vapor variability in the SPR for the time periods L s = 195°–345° in MY24–26. Water vapor behavior in the SPR in MY24 and MY26 exhibits substantial similarity in spatial distribution for the same dates and in temporal variability. Water vapor behavior in MY25 is significantly different from that in MY24 and MY26 with abundances ~30% lower around summer solstice (L s = 270°). We hypothesize that water vapor behavior in MY25 was affected by the Global Dust Storm (GDS) that started at L s ~185° of that year and significantly affected the atmosphere of the whole planet. We speculate that the reduction in the observed vapor abundances in MY25 could have resulted from disruption of the southward atmospheric vapor transport from mid-latitudes by the GDS or from reduction of the rate of desorption of vapor from thawed circumpolar terrains due to changes in surface temperature during the GDS. Through most of the spring, highest vapor abundances are observed just northward of the retreating edge of the seasonal CO 2 cap, with generally low abundances over the seasonal cap. Repeated cycles of condensation and re-sublimation of water vapor on the edge of the retreating cap could be responsible for this build-up of vapor near the cap edge. Relatively high vapor abundances that are systematically observed over some regions of the cap in late spring could be associated with venting of the mixture of water vapor, CO 2 gas and dust from underneath the seasonal cap through fractures in the frost. We explore the evolution of the water vapor in the SPR during spring and summer using two 1-dimenional models representing two limiting cases that attribute observed changes to either atmospheric transport or surface sources. The atmospheric transport model appears to be more consistent with observations, suggesting that atmospheric transport plays the dominant role in the water vapor cycle in the SPR. However, activity of surface processes such as desorption of vapor from the regolith cannot be excluded. Comparison of the water vapor cycle during spring and summer in the SPR and the Northern Polar Region (NPR) shows that, besides the difference in the highest observed abundances, the evolution of the vapor abundances shows remarkable qualitative similarity, despite the presence of a large source of vapor during summer in the north in the form of the North Polar Residual Cap (NPRC). This suggests that the processes shaping the water cycle in the polar regions are similar in nature and differ only in strength. The new data on water vapor in the SPR, together with our previous retrievals of water vapor in the NPR, constitute a new dataset that enables testing of Martian Global Circulation Models close to the planet's poles, and enables better understanding of the difference between the Martian polar regions. • Water vapor abundances in the Martian polar atmosphere retrieved for spring and summer seasons in MY24-26. • Atmospheric transport appears to play the dominant role in the water cycle at the southern polar region (SPR). • Seasonal changes and spatial distributions of vapor abundances are similar in MY24 and MY26. • Vapor abundances are 30% lower in MY25 following the global dust storm of MY25, representing substantial interannual variability. • The dust storm of MY25 could have reduced atmospheric transport of vapor to the SPR and/or reduced desorption of water from soil in the SPR. [ABSTRACT FROM AUTHOR]

Using a combination of orbital and surface observations, we constrain the seasonal vertical distribution of water vapor in the planetary boundary layer in the lowest scale-height of the Martian atmosphere at the Phoenix Mars Lander location (68°N, 234°E). Previous observations have shown significant discrepancies regarding the vapor distribution in the boundary layer, drawing conflicting conclusions as to whether water is uniformly mixed below the cloud condensation height, or whether water is mostly confined in the near surface layer. We conclude that the uniformly well-mixed assumption for water vapor up to the cloud condensation level is not always compatible with observational constraints, particularly when peak near-surface water vapor abundances are observed during L s = 110°–120°. The uniformly well-mixed assumption leads to an over-estimation of the total water vapor column abundances between L s = 80°–120°, and an under-estimation of the total water vapor column abundances between L s = 120°–150°. The overestimation of vapor in the column is particularly evident during peak surface water vapor pressures (∼L s = 110°–120°), suggesting a concentration of water vapor at the surface that actively participates in subsurface exchange. Using both TECP and column vapor abundance as constraints for the vertical vapor distribution, the maximum height of the well-mixed vapor layer ranges between ∼3.5–13.5 km, all of which falls below the cloud condensation height for the corresponding season. From L s = 120° to 150°, the maximum height of the well-mixed layer stays fairly consistent at a mean height of ∼7 km. These results are particularly important for providing insight into the seasonal transport of water and the role of regolith-atmospheric exchange. • Relative humidity along with column abundances are used to constrain the seasonally varying vertical extent of water vapor. • We conclude that water is mostly confined in the near surface layer, rather than uniformly well-mixed, as commonly assumed. • Near-surface enhancement of water suggests daytime convection is insufficient to mix water up to the cloud condensation level. [ABSTRACT FROM AUTHOR]

Atmospheric limb sounding is a well-established technique for measuring atmospheric temperature, composition, and wind. The theoretical capabilities of a submillimeter limb sounder placed in low Mars orbit are quantified, with a particular focus on the ability to make profile measurements of line-of-sight wind, temperature, water vapor, deuterated water vapor, several isotopes of carbon monoxide, oxygen-18 carbon dioxide, ozone, and hydrogen peroxide. We identify cases where all such measurements can be made within a single 25–70 GHz wide region of the submillimeter spectrum, enabling use of a single state-of-the-art submillimeter receiver. Six potential spectral regions, approximately centered at 335 GHz, 450 GHz, 550 GHz, 900 GHz, 1000 GHz, and 1130 GHz are found, any one of which can provide a complete measurement suite. The expected precision and vertical resolution of temperature, composition, and wind measurements from instruments in each range are quantified. This work thus follows on from that of Urban et al. (2005), Kasai et al. (2012), and earlier studies, expanding them to consider many alternative observing frequency regions. In general, performance (in terms of measurement precision and vertical resolution) is improved with increasing observation frequency. In part this is due to our choice to assume the same antenna size for each frequency, thus providing a narrower field of view for the higher frequency configurations. The general increase in emission line strengths with increasing frequency also contributes to this improved performance in some cases. However, increased instrument power needs for the higher frequency configurations may argue against their choice in some mission scenarios. [ABSTRACT FROM AUTHOR]

We used Phoenix Surface Stereo Imager data, constrained by other Phoenix and MRO data taken via a planned coordinated measurement campaign, along with radiative transfer modeling to assess the vertical water vapor profile at the Phoenix arctic location during its spring and summer mission. We examined 16 mid-afternoon observations spanning L s = 97.5°–148°. We developed a 2-layer model of vapor distribution which reproduces the water vapor band depth. Using the results of the 2-layer model, we retrieved the mass mixing ratios in each layer and the implied surface vapor pressure. We found that near surface water vapor was enhanced relative to higher layers, resulting in a large percentage of the water column (>25% and up to nearly 100%) confined below ~2.5 km. • Radiative transfer analysis of Phoenix images taken with a water vapor band is presented. • Water vapor is confined near the surface and not well mixed in the boundary layer. • Mechanisms for confining water vapor near the surface are suggested. [ABSTRACT FROM AUTHOR]

Diurnal and annual water cycles are studied during the first year of Perseverance rover in Jezero, using observations from the Mars Environmental Dynamics Analyzer (MEDA) and column modeling. Areal values for the ground thermal inertia (TI) and albedo are first found at one site by fitting model temperatures to the observed air temperatures. Areal soil porosity and the initial water vapor volume mixing ratios (vmr) are next found via model-vmr fits to the observation-based vmr. The meteorology and physics of the modeled air and subsurface diurnal moisture cycle at the site is then discussed in detail. The process of fit to observations is finally extended to fourteen sites along the Perseverance track, resulting in estimates for areal TI, albedo and porosity at these sites, and in MEDA-based initial estimates for the annual and diurnal moisture cycles at Jezero during MY36. • MEDA diurnal observations and column model are compared at 14 sites in Jezero. • Fits to MEDA air temperatures provide model values for areal TI and albedo. • Fits to MEDA air moistures provide model values for areal porosity and column water. • Meteorology and physics of the diurnal moisture cycle is described in detail. • Annual site-by-site results appear to agree with satellite retrievals. [ABSTRACT FROM AUTHOR]