Ventifacts, rocks abraded by wind‐borne particles, are found in Gale Crater, Mars. In the eastward drive from “Bradbury Landing” to “Rocknest,” they account for about half of the float and outcrop ...seen by Curiosity's cameras. Many are faceted and exhibit abrasion textures found at a range of scales, from submillimeter lineations to centimeter‐scale facets, scallops, flutes, and grooves. The drive path geometry in the first 100 sols of the mission emphasized the identification of abrasion facets and textures formed by westerly flow. This upwind direction is inconsistent with predictions based on models and the orientation of regional dunes, suggesting that these ventifact features formed from very rare high‐speed winds. The absence of active sand and evidence for deflation in the area indicates that most of the ventifacts are fossil features experiencing little abrasion today.
Key Points
Ventifacts in Gale Crater
May be formed by paleowind
Can see abrasion textures at range of scales
The first of the two missions foreseen in the ExoMars program was successfully launched on 14th March 2016. It included the Trace Gas Orbiter and the Schiaparelli Entry descent and landing ...Demonstrator Module. Schiaparelli hosted the DREAMS instrument suite that was the only scientific payload designed to operate after the touchdown. DREAMS is a meteorological station with the capability of measuring the electric properties of the Martian atmosphere. It was a completely autonomous instrument, relying on its internal battery for the power supply. Even with low resources (mass, energy), DREAMS would be able to perform novel measurements on Mars (atmospheric electric field) and further our understanding of the Martian environment, including the dust cycle. DREAMS sensors were designed to operate in a very dusty environment, because the experiment was designed to operate on Mars during the dust storm season (October 2016 in Meridiani Planum). Unfortunately, the Schiaparelli module failed part of the descent and the landing and crashed onto the surface of Mars. Nevertheless, several seconds before the crash, the module central computer switched the DREAMS instrument on, and sent back housekeeping data indicating that the DREAMS sensors were performing nominally. This article describes the instrument in terms of scientific goals, design, working principle and performances, as well as the results of calibration and field tests. The spare model is mature and available to fly in a future mission.
Atmospheric aerosols produce both a direct radiative forcing by scattering and absorbing solar and infrared radiation, and an indirect radiative forcing by altering cloud processes. Therefore, it is ...essential to understand the physical processes that contribute to the global aerosol budget. The International Panel on Climate Change (IPCC) reports that mineral dust contributes to ∼1/3 of all primary particle emissions to the atmosphere. The significance of mineral dust aerosol becomes evident when one considers the large surface area of arid and semi‐arid regions on most continents. It is evident from observations in the U.S. Southwest that convective plumes and vortices lift large quantities of desert dust. Here, we use a combination of observational data and theory to determine the role of convective plumes and vortices on the global aerosol budget. We show that convective plumes and vortices contribute to about 35% of the global budget of mineral dust.
Dust devils as observed by Mars Pathfinder Ferri, Francesca; Smith, Peter H.; Lemmon, Mark ...
Journal of Geophysical Research - Planets,
December 2003, Letnik:
108, Številka:
E12
Journal Article
Recenzirano
Odprti dostop
Dust devils are localized meteorological phenomena frequently observed in terrestrial dry lands and desert landscapes as well as on Mars. They are low‐pressure, warm core vortices that form at the ...bottom of convective plumes and loft dust from the surface. They move with the speed of the ambient wind and are tilted by wind shears. The Mars Pathfinder detected dust devils as dust plumes in the Imager for Mars Pathfinder images and as low‐pressure convective vortices in the meteorological Mars Pathfinder Atmospheric Structure Investigation/Meteorology (ASI/MET) experiment data. The Pathfinder data have been analyzed in terms of dust devil size, spatial distribution, and frequency of occurrence. The results show that the Pathfinder imaging and MET observations are consistent with each other and with the observations made by the Viking 1 Orbiter and Mars Global Surveyor. The dust devil's ability to loft dust into the atmosphere has been investigated and a thermodynamic theory for dust devils has been used to calculate their physical parameters relevant to dust transport. The dust devils observed in an active day provide a pumping rate larger than the dust‐settling rate derived from the optical obscuration of the Pathfinder rover solar panels. Therefore dust devils are a major factor in transporting dust from the surface to the atmosphere at the Pathfinder site.
In situ measurements of relative humidity (RH) on Mars have only been performed by the Phoenix (PHX) and Mars Science Laboratory (MSL) missions. Here we present results of our recalibration of the ...PHX thermal and electrical conductivity probe (TECP) RH sensor. This recalibration was conducted using a TECP engineering model subjected to the full range of environmental conditions at the PHX landing site in the Michigan Mars Environmental Chamber. The experiments focused on the warmest and driest conditions (daytime) because they were not covered in the original calibration (Zent et al., 2010, https://doi.org/10.1029/2009JE003420) and previous recalibration (Zent et al., 2016, https://doi.org/10.1002/2015JE004933). In nighttime conditions, our results are in excellent agreement with the previous 2016 recalibration, while in daytime conditions, our results show larger water vapor pressure values. We obtain vapor pressure values in the range ~0.005–1.4 Pa, while Zent et al. (2016, https://doi.org/10.1002/2015JE004933) obtain values in the range ~0.004–0.4 Pa. Our higher daytime values are in better agreement with independent estimates from the ground by the PHX Surface Stereo Imager instrument and from orbit by Compact Reconnaissance Imaging Spectrometer for Mars. Our results imply larger day‐to‐night ratios of water vapor pressure at PHX compared to MSL, suggesting a stronger atmosphere‐regolith interchange in the Martian arctic than at lower latitudes. Further, they indicate that brine formation at the PHX landing site via deliquescence can be achieved only temporarily between midnight and 6 a.m. on a few sols. The results from our recalibration are important because they shed light on the near‐surface humidity environment on Mars.
Key Points
We have recalibrated the relative humidity sensor of the Mars Phoenix lander
We obtain water vapor pressure values in the range ~0.005–1.4 Pa, while in previous recalibrations, values in the range ~0.004–0.4 Pa
Our results show a two‐order‐of‐magnitude diurnal variation of water vapor pressure, suggesting a strong atmosphere‐regolith interchange
Plain Language Summary
We present our recalibration of Phoenix's humidity sensor. This recalibration was conducted with a copy of the sensor subjected to the environmental conditions at the Phoenix landing site. Our experiments focus on the warmest and driest conditions because they were not covered in previous calibrations. Our recalibration shows daytime water content values one order of magnitude larger than those in the previous calibration. At nighttime conditions, our results are in excellent agreement with the previous calibration. Our higher daytime values are in better agreement with independent estimates from the ground, and from orbit. Our results imply larger diurnal variations of water content at Phoenix compared to Curiosity, suggesting a stronger atmosphere‐soil interchange in the Martian arctic than at lower latitudes. Further, they indicate that environmental conditions favorable for the formation of saline solutions (brine) are only achieved temporarily between midnight and 6 a.m. on a few Martian days. The results from our recalibration are important because measurements of humidity on the Martian surface are needed to shed light on the local and global water cycle of Mars, and so far, only the Phoenix mission in the arctic region and the Curiosity rover at equatorial latitudes have performed such measurements.
Two recalibrated sets of Phoenix (PHX) near-surface TECP air humidity measurements were compared with results from adsorptive single column model simulations during a warm clear-sky polar midsummer ...period, PHX sols 50–60. The model's 2 m temperatures were close to the observed values. Relative humidity (RH) is very low during the day but at night RH at 2 m reaches nearly 100% by the Zent et al. (2016) recalibration (Z), and 60–70% by the Fischer et al. (2019) recalibration (F). Model values of RH2m are close to Z and F at night and to F during the day. All three imply low water vapor pressures near the surface at night, 0.03–0.05 Pa, with a rapid increase each morning to 0.3–1 Pa and a decrease in the evening by both F and the model simulation. The model's daily adsorbed and desorbed water is in balance for regolith porosity of 16% (instead of 35% for lower latitudes). The depleted layer of nighttime air moisture extends to only about 200 m above the surface; hence the model's precipitable water content stays around the observed ~30 μm throughout the sol. The model's moisture cycle is not sensitive to tortuosity of the regolith but the in-pore molecular diffusivity should be at least 5 cm2/s for fair agreement with the observations. In the adsorption experiments there is no fog and just a hint of ground frost, as observed during this period. Strong night frosts appear if adsorption is made weak or absent in the model.
•Two Phoenix TECP air humidity observation sets are compared with adsorptive column model simulations for PHX sols 50-60.•At night RH at 2 m hits nearly 100% by the Zent 2016 recalibration and model, and 60% by the Fischer 2019 recalibration.•During the night water vapor pressure is low (~0.04 Pa) by all three but rises to ~0.4 Pa each morning by the Fischer recalibration and model.•Model-indicated average porosity is 16% for regolith around Phoenix.•Strong night frosts appear if adsorption is made weak or absent in the model.
The cloud-mediated aerosol radiative forcing is widely recognized as the main source of uncertainty in our knowledge of the anthropogenic forcing on climate. The current challenges for improving our ...understanding are (1) global measurements of cloud condensation nuclei (CCN) in the cloudy boundary layer from space, and (2) disentangling the effects of aerosols from the thermodynamic and meteorological effects on the clouds. Here, we present a new conceptual framework to help us overcome these two challenges, using relatively simple passive satellite measurements in the visible and infared (IR). The idea is to use the clouds themselves as natural CCN chambers by retrieving simultaneously the number of activated aerosols at cloud base, Na, and the cloud base updraft speed. The Na is obtained by analyzing the distribution of cloud drop effective radius in convective elements as a function of distance above cloud base. The cloud base updraft velocities are estimated by double stereoscopic viewing and tracking of the evolution of cloud surface features just above cloud base. In order to resolve the vertical dimension of the clouds, the field of view will be 100 m for the microphysical retrievals, and 50 m for the stereoscopic measurements. The viewing geometry will be eastward and 30 degrees off nadir, with the Sun in the back at 30 degrees off zenith westward, requiring a Sun-synchronous orbit at 14 LST. Measuring simultaneously the thermodynamic environment, the vertical motions of the clouds, their microstructure and the CCN concentration will allow separating the dynamics from the CCN effects. This concept is being applied in the proposed satellite mission named Clouds, Hazards and Aerosols Survey for Earth Researchers (CHASER).
Based on the heat engine framework, a simple scaling theory for dust devils is proposed and compared to observations. This theory provides a simple physical interpretation for many of the observed ...characteristics of dust devils.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We use in situ environmental measurements by the Mars Science Laboratory (MSL) mission to obtain the surface energy budget (SEB) across Curiosity's traverse during the first 2500 sols of the mission. ...This includes values of the downwelling shortwave solar radiation, the upwelling solar radiation reflected by the surface, the downwelling longwave radiation from the atmosphere, the upwelling longwave radiation emitted by the surface, the sensible heat flux associated with turbulent motions, and the latent heat flux associated with water phase changes. We then analyze their temporal variation on different timescales and relate this to the mechanisms causing these variations. Through its Rover Environmental Monitoring Station, MSL allows for a more accurate determination of the SEB than its predecessors on Mars. Moreover, the unprecedented duration, cadence, and frequency of MSL environmental observations allow for analyses of the SEB from diurnal to interannual timescales. The results presented in this article can be used to evaluate the consistency with predictions from atmospheric numerical models, to validate aerosol radiative properties under a range of dust conditions, to understand the energy available for solar‐powered missions, and to enable comparisons with measurements of the SEB by the Perseverance rover at Jezero crater.
Plain Language Summary
The primary energy input at the Martian surface is the solar radiation, which depends on the time of the day and season, geographical location (latitude and altitude), and atmospheric dust and gas abundances. Another energy input is the thermal atmospheric forcing, which depends on the vertical distribution of dust and water ice aerosols as well as CO2 and H2O molecules. Together with the reflected solar radiation and the thermal radiation emitted by the surface, these four terms make up the net radiative forcing of the surface. In response to it, energy outputs as turbulent motions and water phase changes emerge to cool down/warm up the ground. The remaining energy is available to control the thermal environment in the surface and shallow subsurface through conduction into the soil. By using first‐of‐their‐kind measurements from the Mars Science Laboratory mission, we calculate the energy inputs and outputs across Curiosity's traverse over the first 2500 Martian days of the mission. We then analyze their temporal variations and relate this to the mechanisms causing such variations. An accurate determination of the surface energy budget is key to preparing for the human exploration of Mars because it contributes to improvements in the predictive capabilities of numerical models.
Key Points
We have calculated each term of the surface energy budget during the first 2500 sols of the Mars Science Laboratory mission
We have analyzed the variation of each term from diurnal to interannual timescales in relation to the mechanisms causing the variations
Our results are important in preparation for the human exploration of Mars to evaluate the consistency with predictions from models
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