Search

Since leaving Vera Rubin ridge (VRr), the Mars Science Laboratory Curiosityrover has traversed though the phyllosilicate‐bearing region, Glen Torridon, and the overlying Mg‐sulfate‐bearing strata, with excursions onto the Greenheugh Pediment and Amapari Marker Band. Each of these distinct geologic units were investigated using Curiosity's Mast Camera (Mastcam) multispectral instrument which is sensitive to iron‐bearing phases and some hydrated minerals. We used Mastcam spectra, in combination with chemical data from Chemistry and Mineralogy, Alpha Particle X‐ray Spectrometer, and Chemistry and Camera instruments, to assess the variability of rock spectra and interpret the mineralogy and diagenesis in the clay‐sulfate transition and surrounding regions. We identify four new classes of rock spectra since leaving VRr; two are inherent to dusty and pyroxene‐rich surfaces on the Amapari Marker Band; one is associated with the relatively young, basaltic, Greenheugh Pediment; and the last indicates areas subjected to intense aqueous alteration with an amorphous Fe‐sulfate component, primarily in the clay‐sulfate transition region. To constrain the Mg‐sulfate detection capabilities of Mastcam and aid in the analyses of multispectral data, we also measured the spectral response of mixtures with phyllosilicates, hydrated Mg‐sulfate, and basalt in the laboratory. We find that hydrated Mg‐sulfates are easily masked by other materials, requiring ≥90 wt.% of hydrated Mg‐sulfate to exhibit a hydration signature in Mastcam spectra, which places constraints on the abundance of hydrated Mg‐sulfates along the traverse. Together, these results imply significant compositional changes along the traverse since leaving VRr, and they support the hypothesis of wet‐dry cycles in the clay‐sulfate transition. The clay‐sulfate transition in Gale crater has long been hypothesized to record an environmental shift from “warm and wet” to “cold and dry.” The paleolake that once filled Gale crater allowed phyllosilicates to form. As Mars became cooler and drier, sulfates were able to precipitate above the phyllosilicates. This mineralogic transition has been observed in other places on Mars, implying a global environmental change. Different hydrated Mg‐sulfates can reveal characteristics of the paleoenvironment at the time of deposition and thus clarify the geologic history. The goals of this study are to (a) characterize potential sulfate‐bearing rocks with the Curiosityrover's multispectral imaging instrument, Mastcam; and (b) constrain Mastcam's Mg‐sulfate detection threshold using laboratory techniques. We identify three new rock spectral classes inherent to the clay‐sulfate transition and one new class associated with the Greeneheugh pediment. Our laboratory results indicate that it would be challenging to detect Mg‐sulfate with Mastcam unless it is nearly pure. New rock spectral classes correspond to unique geologic units. One supports the hypothesis of wet‐dry cycles in the clay‐sulfate transitionCross instrument analyses imply that Mg‐ and Fe‐ sulfates are significant in the amorphous component of the clay‐sulfate transition regionThe spectral signature of hydrated Mg‐sulfates in visible to near infrared reflectance spectra are easily masked by phyllosilicates and/or basalt New rock spectral classes correspond to unique geologic units. One supports the hypothesis of wet‐dry cycles in the clay‐sulfate transition Cross instrument analyses imply that Mg‐ and Fe‐ sulfates are significant in the amorphous component of the clay‐sulfate transition region The spectral signature of hydrated Mg‐sulfates in visible to near infrared reflectance spectra are easily masked by phyllosilicates and/or basalt

During stable conditions, simulated sensible heat fluxes, Qh, in land models exhibit a wide range of behavior, with some models decoupling the atmosphere and land surface, while others continue turbulent exchange. This behavior is dictated by the representation of stability within the model. We explicitly test the representation of Qhduring stable conditions using observed surface temperature, air temperature, and wind speed at the Shallow Cold Pool (SCP) Experiment site in Colorado, USA. This site is characterized by frequent stable conditions and weak‐wind conditions, which are known to be difficult to represent in turbulence schemes. We test the log‐linear, Louis, Holtslag and de Bruin, Beljaar and Holtslag, and Cheng and Brutsaert stability schemes against the observations at the SCP site. We also evaluate the minimum conductance assumption commonly implemented in land models. Simulated Qhbiases are generally small, due largely to compensating errors. Parameterizations could represent Qhin strong‐wind conditions and during the transition from a weak‐ to strong‐wind regime. The behavior of simulated Qhduring strong winds was controlled by the aerodynamic surface roughness, z0. All models, except those that maintain a minimum conductance, were unable to represent turbulence in the weak‐wind regime. We discuss the interacting roles of countergradient fluxes, intermittent turbulence, and decoupled turbulence during this regime. Finally, we list the characteristics that a turbulence parameterization should include and recommend that land models should include a minimum conductance to simulate Qhin the weak‐wind regime. A broad range of turbulence schemes all struggled with representing turbulence in stable conditionsEvaluation of turbulence regimes highlighted missing physics within land model turbulence schemesA minimum conductance in land model turbulence schemes is justified

NASA's Mars‐2020 Perseverance rover spent its first year in Jezero crater studying the mafic lava flows of the Máaz formation and the ultramafic cumulates of the Séítah formation, both of which have undergone minor alteration and are variably covered by coatings, dust, and/or soil deposits. Documenting the rock and soil characteristics across the crater floor is critical for establishing the geologic context of Perseverance's cached samples—which will eventually be returned to Earth—and for interpreting the deposition and modification of the Máaz and Séítah formations. Mastcam‐Z, a pair of multispectral, stereoscopic zoom‐lens cameras, provides broadband red/green/blue and narrowband visible to near‐infrared images (VNIR, 440–1,020 nm). From multispectral observations from sols 0 to 380, we compiled a database of ∼2,400 representative Mastcam‐Z spectra. We analyzed principal components, spectral parameters, and laboratory spectra of pure minerals and natural rock surfaces to interpret the spectral diversity of rocks and soils. We define eight spectral classes of rocks: Dusty, Hematite‐like, Coated, Low‐Ca Pyroxene‐like, Olivine‐like, Weathered Olivine‐like, Fe‐rich Pyroxene‐like, and Dark Oxide‐like. The variability of soil spectra in the Jezero crater floor is controlled primarily by the amount of dust and indicates a largely consistent soil mineralogy across the traverse, with the exception of the area disturbed by the landing event. In comparison to rock spectra from the Curiosity rover's Mastcam instrument in Gale crater, rocks on the Jezero crater floor are generally less spectrally diverse, but the Olivine‐like rocks within the Séítah formation represent a new spectral rock class in Mars surface exploration. NASA's Mars‐2020 Perseverance rover spent its first year in Jezero crater studying rocks that formed in lava flows. These rocks were altered slightly by small amounts of water and are covered with dust and other coatings. Understanding these rocks, and the soils across Perseverance's traverse, is important for two reasons: Perseverance has collected rock and soil samples, which will be the first samples from Mars to be sent back to Earth, and they give insights into the history of Jezero crater. Here, we describe a database of spectra that we compiled from the Mastcam‐Z instrument, which is a pair of science cameras on Perseverance's mast. We analyzed ∼2,400 spectra representing the diversity of rocks and soils across the first 380 Martian days of the mission. We find that the amount of dust in the soils controls their spectral variability. We define eight classes of rock spectra, which are controlled by varying amounts of pyroxenes, olivines, hematite, and other oxides. Compared to spectra from the Mastcam instrument, which documented the Curiosity traverse in Gale crater, the Mastcam‐Z spectra are generally less diverse. However, the Mastcam‐Z spectra of olivine‐like rocks are new, as they have not been previously encountered on Mars. We compiled a database of Mastcam‐Z spectra from the first 380 sols of Perseverance's mission in the floor of Jezero crater, MarsSoil spectral variability is controlled primarily by amounts of dust and indicates a largely consistent soil mineralogy across the traverseRock spectral variability is controlled by varying amounts of pyroxenes, olivines, hematite, and other oxides We compiled a database of Mastcam‐Z spectra from the first 380 sols of Perseverance's mission in the floor of Jezero crater, Mars Soil spectral variability is controlled primarily by amounts of dust and indicates a largely consistent soil mineralogy across the traverse Rock spectral variability is controlled by varying amounts of pyroxenes, olivines, hematite, and other oxides

In the morning, the nocturnal stable boundary layer, SBL, transitions into its daytime convective counterpart substantially impacting the distribution of temperature, humidity, and pollutants. Applying distributed temperature sensing (DTS) below a tethered balloon (2–200 m) and along a tower (0–11 m), for the first time we observed three morning transitions (MTs) in a mountain boundary layer with high temporal (<10 s) and spatial (<0.25 m) resolutions. We show that MTs are best derived from a change in static stability from synchronous DTS observations. Our findings confirm that the MT occurs at the SBL top and bottom simultaneously, and identify horizontal heat advection as a main driver aiding solar surface heating in this midrange mountain valley. We conclude that heterogenous land use and mountainous topography cause complex interactions between valley‐scale and local airflows leading to thermal signatures characterized by strong, small‐scale variability. Our study highlights DTS as a crucial tool for investigating complex thermodynamic processes. On calm nights, a nocturnal stable boundary layer forms near the Earth's surface characterized by increasing temperatures with height and very little mixing. Its counterpart is the daytime convective boundary layer, CBL, which has the opposite characteristics. Both the stable and convective boundary layers have received much attention; however, the in‐between morning transition (MT) has received less attention, which can degrade weather and air quality forecasts. To better understand the morning transition, we measured air temperature below a tethered balloon and on a tower during the MT with a technique called distributed temperature sensing (DTS) using thin fiber‐optic cables. Our unique design enabled an unprecedented view of the MT revealing its detailed and fast‐changing structure. The morning transition is a highly variable process whose theoretical description and experimental investigation had previously been simplified due to observational limitations. We found that it starts simultaneously at the top and bottom of the stable layer, and can take an hour to complete. It is strongly influenced by the surrounding land. While more work using DTS is necessary to understand why the air takes so long to respond to the rising sun, we demonstrate how critical this technique is for future research. A novel technique, distributed temperature sensing (DTS) below a tethered balloon, reveals unknown details of the morning transitionThe morning transition, despite its strong spatiotemporal variability, is robustly determined by changes in static stabilityDTS provides first evidence that the transition occurs simultaneously at the stable boundary bottom and top, and is subject to advection and counter‐gradient flux A novel technique, distributed temperature sensing (DTS) below a tethered balloon, reveals unknown details of the morning transition The morning transition, despite its strong spatiotemporal variability, is robustly determined by changes in static stability DTS provides first evidence that the transition occurs simultaneously at the stable boundary bottom and top, and is subject to advection and counter‐gradient flux

Air flows may be decoupled from the underlying surface either due to strong stratification of air or due to canopy drag suppressing cross‐canopy mixing. During decoupling, turbulent fluxes vary with height and hence identification of decoupled periods is crucial for the estimation of surface fluxes with the eddy covariance (EC) technique and computation of ecosystem‐scale carbon, heat, and water budgets. A new indicator for identifying the decoupled periods is derived using forces (buoyancy and canopy drag) hindering movement of a downward propagating air parcel. This approach improves over the existing methods since (1) changes in forces hindering the coupling are accounted for, and (2) it is based on first principles and not on ad hoc empirical correlations. The applicability of the method is demonstrated at two contrasting EC sites (flat open terrain, boreal forest) and should be applicable also at other EC sites above diverse ecosystems (from grasslands to dense forests). Air flows may be disconnected (i.e., decoupled) from the surface below, meaning that the properties of the flow (e.g., wind speed, temperature, concentrations of gases, pollutants, or particles) do not react to changes at the surface. During these periods, air temperatures near the ground decrease and concentrations of gases, pollutants and particles increase significantly since they are not transported upwards, but rather stay close to the ground. These decoupling periods can take place when the air is strongly stratified (e.g., clear sky, weak wind nights) or thick forest canopies inhibit air mixing. Controls on flow decoupling are poorly understood, yet the phenomenon has significance for scientific monitoring networks and also for the general public due to its connection for example, to air quality and frost formation. In this study, we derive a new indicator for flow decoupling, demonstrate its applicability at two measurement sites and discuss variables controlling decoupling in the light of this new indicator. A universal indicator for air flow vertical decoupling is derivedThe indicator enables analytical estimation of flow decoupling dependency on height, stratification, and leaf area indexThe indicator should be applicable at most flux measurement sites, since it relies only on basic micrometeorological measurements A universal indicator for air flow vertical decoupling is derived The indicator enables analytical estimation of flow decoupling dependency on height, stratification, and leaf area index The indicator should be applicable at most flux measurement sites, since it relies only on basic micrometeorological measurements