We have reconstructed longitude‐latitude maps of column dust optical depth (CDOD) for Martian year (MY) 34 (5 May 2017– 23 March 2019), using observations by the Mars Climate Sounder (MCS) aboard ...NASA's Mars Reconnaissance Orbiter spacecraft. Our methodology works by gridding a combination of standard (v5.2) and novel (v5.3.2) estimates of CDOD from MCS limb observations, using an improved “Iterative Weighted Binning.” In this work, we have produced four gridded CDOD maps per sol, at different Mars Universal Times. Together with the seasonal and daily variability, the use of several maps per sol also allows us to explore the diurnal variability of CDOD in the MCS dataset, which is shown to be particularly strong during the MY 34 equinoctial global dust event (GDE). In order to understand whether the diurnal variability of CDOD has a physical explanation, and examine the impact of the MY 34 GDE on some aspects of the atmospheric circulation, we have carried out numerical simulations with the “Laboratoire de Météorologie Dynamique” Mars Global Climate Model. We show that the model is able to account for at least part of the observed CDOD diurnal variability. This is particularly true in the southern hemisphere where a strong diurnal wave at the time of the GDE is able to displace dust horizontally as well as vertically. The simulations also clearly show the impact of the MY 34 GDE on the mean meridional circulation and the super‐rotating equatorial jet, similarly to the effects of the equinoctial GDE in MY 25.
Plain Language Summary
Large dust storms on Mars have dramatic impacts on the entire atmosphere but may also have critical consequences for robotic and future human missions. Therefore, there is compelling need to produce an accurate reconstruction of their spatial and temporal evolution for a variety of applications, including to guide Mars climate model simulations. The Martian year 34 (5 May 2017–23 March 2019) represents a very interesting case because an extreme dust event occurred near the time of the northern autumn equinox, consisting of multiple large dust storms engulfing all longitudes and most latitudes with dust for more than 150 Martian days (“sols”). We have used satellite observations from the Mars Climate Sounder instrument aboard NASA's Mars Reconnaissance Orbiter to reconstruct longitude‐latitude maps of the opacity of the atmospheric column due to the presence of dust at several times in each sol of Martian year 34. These maps allow us to analyze the seasonal, day‐to‐day, and day‐night variability of dust in the atmospheric column, which is particularly intense during the extreme dust event. We have also used simulations with a Mars climate model to show that the strong day‐night variability may be partly explained by the large‐scale circulation.
Key Points
We reconstruct subdaily maps of column dust optical depth for Martian year 34 to be used for data analysis and modeling
We observe seasonal, daily, and diurnal variability in the column dust, notably during the global dust event (GDE)
Simulations with a global climate model examine the impact of the GDE on the atmospheric circulation and diurnal variability of column dust
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The climate of Mars likely evolved from a warmer, wetter early state to the cold, arid current state. However, no solutions for this evolution have previously been found to satisfy the observed ...geological features and isotopic measurements of the atmosphere. Here we show that a family of solutions exist, invoking no missing reservoirs or loss processes. Escape of carbon via CO photodissociation and sputtering enriches heavy carbon ((13)C) in the Martian atmosphere, partially compensated by moderate carbonate precipitation. The current atmospheric (13)C/(12)C and rock and soil carbonate measurements indicate an early atmosphere with a surface pressure <1 bar. Only scenarios with large amounts of carbonate formation in open lakes permit higher values up to 1.8 bar. The evolutionary scenarios are fully testable with data from the MAVEN mission and further studies of the isotopic composition of carbonate in the Martian rock record through time.
Gravity waves in Mars’s atmosphere strongly affect the general circulation as well as middle atmospheric cloud formation, but the climatology and sources of gravity waves in the lower atmosphere ...remain poorly understood. At Earth, the statistical variance in satellite observations of thermal emission above the instrumental noise floor has been used to enable measurement of gravity wave activity at a global scale. Here is presented an analysis of variance in calibrated radiance at 15.4μm (635–665 cm−1) from off-nadir and nadir observations by the Mars Climate Sounder (MCS) on board Mars Reconnaissance Orbiter (MRO); a major expansion in the observational data available for validating models of Martian gravity wave activity. These observations are sensitive to gravity waves at 20–30 km altitude with wavelength properties (λh=10–100 km, λz> 5 km) that make them likely to affect the dynamics of the middle and upper atmosphere. We find that: (1) strong, moderately intermittent gravity wave activity is scattered over the tropical volcanoes and throughout the middle to high latitudes of both hemispheres during fall and winter, (2) gravity wave activity noticeably departs from climatology during regional and global dust storms; and (3) strong, intermittent variance is observed at night in parts of the southern tropics during its fall/winter, but frequent CO2 ice clouds prevents unambiguous attribution to GW activity. The spatial distribution of wave activity is consistent with topographic sources being dominant, but contributions from boundary layer convection and other convective processes are possible.
•Lower atmospheric gravity wave activity surveyed from orbit over multiple Mars Years.•Gravity wave activity common over tropical volcanoes and winter westerly jets.•Boundary layer convection likely source of gravity wave activity elsewhere.•Gravity wave activity departs from climatology during large dust storms.•Gravity waves and thick mesospheric clouds hard to disambiguate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
High-grade epithelial ovarian carcinomas containing mutated
or
(
) homologous recombination (HR) genes are sensitive to platinum-based chemotherapy and PARP inhibitors (PARPi), while restoration of ...HR function due to secondary mutations in
has been recognized as an important resistance mechanism. We sequenced core HR pathway genes in 12 pairs of pretreatment and postprogression tumor biopsy samples collected from patients in ARIEL2 Part 1, a phase II study of the PARPi rucaparib as treatment for platinum-sensitive, relapsed ovarian carcinoma. In 6 of 12 pretreatment biopsies, a truncation mutation in
, or
was identified. In five of six paired postprogression biopsies, one or more secondary mutations restored the open reading frame. Four distinct secondary mutations and spatial heterogeneity were observed for
complementation assays and a patient-derived xenograft, as well as predictive molecular modeling, confirmed that resistance to rucaparib was associated with secondary mutations.
Analyses of primary and secondary mutations in
and
provide evidence for these primary mutations in conferring PARPi sensitivity and secondary mutations as a mechanism of acquired PARPi resistance. PARPi resistance due to secondary mutations underpins the need for early delivery of PARPi therapy and for combination strategies.
.
Deep convection, as used in meteorology, refers to the rapid ascent of air parcels in the Earth's troposphere driven by the buoyancy generated by phase change in water. Deep convection undergirds ...some of the Earth's most important and violent weather phenomena and is responsible for many aspects of the observed distribution of energy, momentum, and constituents (particularly water) in the Earth's atmosphere. Deep convection driven by buoyancy generated by the radiative heating of atmospheric dust may be similarly important in the atmosphere of Mars but lacks a systematic description. Here we propose a comprehensive framework for this phenomenon of dusty deep convection (DDC) that is supported by energetic calculations and observations of the vertical dust distribution and exemplary dusty deep convective structures within local, regional, and global dust storm activity. In this framework, DDC is distinct from a spectrum of weaker dusty convective activity because DDC originates from pre-existing or concurrently forming mesoscale circulations that generate high surface dust fluxes, oppose large-scale horizontal advective-diffusive processes, and are thus able to maintain higher dust concentrations than typically simulated. DDC takes two distinctive forms. Mesoscale circulations that form near Mars's highest volcanoes in dust storms of all scales can transport dust to the base of the upper atmosphere in as little as two hours. In the second distinctive form, mesoscale circulations at low elevations within regional and global dust storm activity generate freely convecting streamers of dust that are sheared into the middle atmosphere over the diurnal cycle.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We derive the depth of the water ice table on Mars by fitting seasonal surface temperature trends acquired by the Mars Climate Sounder and Thermal Emission Imaging System with a two‐layer regolith ...model assuming frozen H2O as the lower material. Our results are consistent with widespread water ice at latitudes as low as 35°N/45°S buried sometimes a few centimeters below sand‐like material, with high lateral ice depth variability, and correlated with periglacial features. While several investigations have already predicted, identified, and characterized some properties of near‐surface ice on Mars, our results constitute a significant advance in the context of the upcoming crewed exploration because (1) they focus on very shallow depths accessible with limited equipment, (2) they provide continuous regional coverage including the midlatitudes, and (3) they yield moderate spatial resolution maps (3 ppd) relevant to landing site selection studies.
Plain Language Summary
Frozen water is a very strong heat conductor compared to typical Martian regolith. As a result, near‐surface ice measurably influences seasonal surface temperature trends, and the depth of the H2O table controls the amplitude of this effect. We leverage this influence on orbital temperature observations using a numerical heat transfer model to derive regional and local maps of the ice depth on Mars, at much higher spatial resolution than previously available. We show that water ice is present sometimes just a few centimeters below the surface, at locations where future landing is realistic, under mobile material that could easily be moved around. This ice could be exploited on‐site for drinking water, breathable oxygen, etc., at a much lower cost than if brought from Earth.
Key Points
Shallow subsurface water ice on Mars influences seasonal surface temperatures in a measurable manner with MCS and THEMIS
We leverage this effect to map the depth to the water ice table at middle and high latitudes
Large continuous units of shallow ice are found ~35°N and ~45°S and could be exploited for future crewed missions
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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.
Key Points
The snowiest place in the south polar region is the south polar residual cap
A separate class of small, short‐lived CO2 clouds predominate 70‐80 S
Dusty convection, convective activity powered by radiative heating of dust, is a ubiquitous phenomenon in Mars's atmosphere but is especially deep (i.e., impactful on the middle atmosphere) and ...widespread during planet‐encircling dust events (PEDEs) that occur every few Mars Years (MYs). Yet the relative roles of dusty deep convection and global dynamics, such as the principal meridional overturning cell and the radiative tides, in dust storm development and the vertical transport of dust and water are still unclear. Here, observations from the Mars Climate Sounder on board Mars Reconnaissance Orbiter (MRO‐MCS) are used to study dusty deep convection and its impact on middle atmospheric water content during the MY 34 PEDE (commenced June 2018). Additional context is provided by MRO‐MCS observations of the MY 28 PEDE (commenced June 2007). This investigation establishes that a few, localized centers of dusty deep convection in the tropics formed in the initial phases of both PEDE simultaneously with a substantial increase in middle atmospheric water content. The growth phase of the MY 34 PEDE was defined by episodic outbreaks of deep convection along the Acidalia and Utopia storm tracks as opposed to less episodic, more longitudinally distributed convective activity during the MY 28 PEDE. The most intense convection during both PEDE was observed in southern/eastern Tharsis, where MRO‐MCS observed multiple instances of deep convective clouds transporting dust to altitudes of 70–90 km. These results suggest that Martian PEDE typically contain multiple convectively active mesoscale weather systems.
Plain Language Summary
Just as the heat released by condensing water vapor powers thunderstorms in Earth's atmosphere, very dusty air heated by the Sun in Mars's atmosphere can power dust clouds that tower many tens of kilometers. These dust towers are most common in Mars's rare and impressive planet‐encircling dust events, when dust is rapidly lifted from the surface and the planet's atmosphere fills with a thick haze of dust. But the role of dust towers is unknown. In one view, dust towers randomly form from dust lifted by stronger trade winds in the dust event. In another view, the dust towers organize into a few hurricane‐like storms that spread dust around the planet. Here we study the two most recent planet‐encircling dust events in 2007 and 2018. We find that dust towers first form at the same time as a rapid increase in water at high latitudes observed early in each event. In the 2018 storm, dust tower forming weather systems initially formed near the equator along low elevation pathways along which strong cold fronts in the northern hemisphere may have traveled. Dust towers east of Mars's high Tharsis volcanoes were especially strong.
Key Points
Deep convection during the MY 34 PEDE was more episodic than in the MY 28 PEDE
The tallest convective clouds during the MY 34 PEDE were more than 80 km high
Tropical hygropause altitude increased from 55 km to 65–70 km during the initial convective episode, peaking at 75–80 km during a later one
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We have used observations from the Mars Climate Sounder (MCS) to investigate the north polar hood (NPH) water ice clouds, including the first systematic examination of the vertical and nighttime ...structure. We show that the NPH clouds are present between LS = 150° (early autumn) and 30° (late spring) and that the clouds always extend to the pole. The daytime (1500 LMST) and nighttime (0300 LMST) clouds both have one layer that extends in altitude from 10 to 40 km above the surface, and the layer falls from its peak with a constant mixing ratio. We find that the cloud optical depth is controlled by the atmospheric thermal structure. The nighttime optical depth values are often higher than the daytime, sometimes due to tidally driven diurnal temperature differences and other times (i.e., LS = 240°–330°) a result of low temperatures associated with the polar vortex at night. We conclude that polar hood clouds are primarily controlled by the temperature structure and form at the water condensation level.
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 storm
Dust diurnal variability at low and middle latitudes is largely related to the meridional circulation exhibiting diurnal tidal variations
Diurnal variations at south polar latitudes are related to a remnant of the polar vortex confined to the nightside of the planet
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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