Antarctic dry valleys: Microclimate zonation, variable geomorphic processes, and implications for assessing climate change on Mars

The Antarctic Dry Valleys (ADV) are generally classified as a hyper-arid, cold-polar desert. The region has long been considered an important terrestrial analog for Mars because of its generally cold and dry climate and because it contains a suite of landforms at macro-, meso-, and microscales that closely resemble those occurring on the martian surface. The extreme hyperaridity of both Mars and the ADV has focused attention on the importance of salts and brines on soil development, phase transitions from liquid water to water ice, and ultimately, on process geomorphology and landscape evolution at a range of scales on both planets. The ADV can be subdivided into three microclimate zones: a coastal thaw zone, an inland mixed zone, and a stable upland zone; zones are defined on the basis of summertime measurements of atmospheric temperature, soil moisture, and relative humidity. Subtle variations in these climate parameters result in considerable differences in the distribution and morphology of: (1) macroscale features (e.g., slopes and gullies); (2) mesoscale features (e.g., polygons, including ice-wedge, sand-wedge, and sublimation-type polygons, as well as viscous-flow features, including solifluction lobes, gelifluction lobes, and debris-covered glaciers); and (3) microscale features (e.g., rock-weathering processes/features, including salt weathering, wind erosion, and surface pitting). Equilibrium landforms are those features that formed in balance with environmental conditions within fixed microclimate zones. Some equilibrium landforms, such as sublimation polygons, indicate the presence of extensive near-surface ice; identification of similar landforms on Mars may also provide a basis for detecting the location of shallow ice. Landforms that today appear in disequilibrium with local microclimate conditions in the ADV signify past and/or ongoing shifts in climate zonation; understanding these shifts is assisting in the documentation of the climate record for the ADV. A similar type of landform analysis can be applied to the surface of Mars where analogous microclimates and equilibrium landforms occur (1) in a variety of local environments, (2) in different latitudinal bands, and (3) in units of different ages. Documenting the nature and evolution of the ADV microclimate zones and their associated geomorphic processes is helping to provide a quantitative framework for assessing the evolution of climate on Mars.     

Some remarks on the thermodynamics of cyclones and anticyclones

Summary A quantitative theory of steady-state cyclones and anticyclones is based on a thermodynamic cycle, in which the surface frictional flow of air towards low pressure is compensated by an outflow aloft. It is shown that such a steady-state flow can only be sustained by a distribution of heat sources and sinks, depending on the surface windfield, the frictional drag, and the height of the return flow. When the two latter quantities are specified the steady-state surface wind- and pressure-pattern can be inferred from the disposition of heat sources and sinks in the atmosphere.Given the vertical profile of temperature and humidity it is possible to estimate the net heat added to or subtracted from different levels in the atmosphere by radiation processes. If, in addition, the balance between precipitation and evaporation is known, the distribution of sources and sinks in the free atmosphere may be determined, and this procedure may be made largely routine with such aids as the radiation chart. Hence it is possible to infer the structure, intensity and size of an equilibrium surface pressure-field from the computed disposition of sources and sinks in the atmosphere. In the future it should be possible to carry through such an analysis as part of routine forecasting procedure. It is shown that the surface pressure contrast in such monsoonal systems as the Siberian Winter High is of the order called for by the thermodynamic theory. The sustaining source and sink intensities needed for cyclones and anticyclones of average size and pressure-contrast are of the order of those occurring in nature.Cyclones and anticyclones are conveniently classified according to the nature of the sustaining sources or sinks. In particular, shallow systems, cold highs and warm lows are associated with low level sinks or sources, while systems of great vertical extent, warm highs and cold lows, are associated with sinks and sources at high level.

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Zusammenfassung Eine quantitative Theorie stationärer Zyklonen und Antizyklonen wird auf einen thermodynamischen Kreisprozeß, basiert, in dem die reibungsbedingte Luftströmung an der Erdoberfläche gegen das Tiefdruckzentrum durch ein Abfließen in der Höhe kompensiert wird. Es wird gezeigt, daß eine solche stationäre Strömung nur durch eine Verteilung von Wärmequellen und Sinkstellen aufrecht erhalten werden kann, die durch das Windfeld am Boden, die Reibungsverzögerung und die Höhe des Rückkehrstromes bedingt ist. Wenn die zwei letztgenannten Größen bestimmt sind, kann aus der Verteilung der Wärmequellen und Sinkstellen in der Atmosphäre auf das Wind- und Druckfeld des stationären Zustandes am Boden geschlossen werden.Aus dem Vertikalprofil von Temperatur und Feuchtigkeit ist es möglich, den durch Strahlungsvorgänge in verschiedenen Höhen erzeugten Wärmeüberschuß oder-verlust abzuschätzen. Wenn außerdem die Bilanz zwischen Niederschlag und Verdunstung bekannt ist, kann auch die Verteilung der Quellen und Sinkstellen in der Atmosphäre bestimmt werden und dieses Verfahren kann auf Grund von Strahlungskarten Eingang in die tägliche Praxis finden. Damit ist es möglich, aus der berechneten Verteilung von Quellen und Sinkstellen Schlüsse auf die Struktur, die Intensität und die Ausdehnung eines im Gleichgewicht befindlichen Druckfeldes zu ziehen. In Zukunft mag sich auch die Möglichkeit ergeben, eine solche Analyse als Teil des täglichen Wetterdienstes durchzuführen.Es wird gezeigt, daß die Druckunterschiede am Boden in solchen Monsunsystemen wie dem sibirischen Winterhoch von der gleichen Größenordnung sind, wie sie sich aus der thermodynamischen Theorie voraussagen lassen. Die Intensität von Quellen und Sinkstellen, die in der freien Atmosphäre auftreten, hat die richtige Größe, um die Aufrechterhaltung von Zyklonen und Antizyklonen mit den Dimensionen und Druckunterschieden zu erklären, wie sie in der Natur beobachtet werden.Zyklonen und Antizyklonen werden praktischerweise auf Grund der Beschaffenheit der Quellen oder Sinkstellen eingeteilt, die sie aufrecht erhalten. Im speziellen sind seichte Systeme, wie Kältehoch und Wärmetief, mit Quellen oder Sinkstellen im tieferen Niveau verknüpft, während Systeme mit großer Vertikalerstreckung, wie Wärmehoch und Kältetief, mit Quellen oder Sinkstellen in größerer Höhe verbunden sind.

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Résumé On développe une théorie quantitative des dépressions et anticyclones stationnaires sur la base d'un cycle thermodynamique fermé dans lequel le courant soumis au frottement et dirigé vers le centre dépressionnaire est compensé par un écoulement divergent en altitude. On montre qu'un tel système stationnaire ne peut se maintenir que par une répartition des sources et des puits de chaleur conditionnée par le champ de vent au sol, le retard dû au frottement et l'altitude du courant de retour. Si les deux dernières grandeurs sont déterminées, on peut connaître le champ de vent et de pression de l'état stationnaire au sol à partir de la répartition des sources chaudes et des puits dans l'atmosphère.Grâce au profil vertical de température et d'humidité, il est possible d'évaluer l'excès ou le défaut de chaleur produits par les processus radiatifs à différents niveaux. Si en outre le bilan entre les précipitations et l'évaporation est connu, on peut aussi déterminer la distribution des sources et des puits dans l'atmosphère et ce procédé pourra entrer dans le travail de routine à l'aide de cartes de rayonnement. Ainsi il est possible, à partir de la distribution calculée des sources et des puits, de tirer des conclusions sur la structure, l'intensité et l'étendue d'un champ de pression en équilibre. On peut envisager dans l'avenir la possibilité d'adjoindre une telle analyse à la prévision journalière du temps.On montre que les différences de pression au sol dans des systèmes de mousson tels que celui de l'anticyclone hivernal sibérien sont de l'ordre de grandeur prévu par la théorie thermodynamique. L'intensité des sources et des puits qui apparaissent dans l'atmosphère libre a la valeur voulue pour entretenir les dépressions et les anticyclones avec les dimensions et les différences de pression que l'on observe dans la nature.On peut classer les dépressions et les anticyclones d'une manière pratique d'après la nature des sources et des puits qui les entretiennent. En particulier, des systèmes de peu d'épaisseur comme des anticyclones froids et des dépressions chaudes sont liés à des sources et des puits situés à basse altitude; par contre des systèmes de grande ampleur verticale comme des anticyclones chauds et des dépressions froides sont liés à des sources ou des puits à haute altitude.

     

Hydraulic redistribution and hydrological controls on aspen transpiration and establishment in peatlands following wildfire

In the sub‐humid Western Boreal Plains of Alberta, where evapotranspiration often exceeds precipitation, trembling aspen (Populus tremuloides Michx.) uplands often depend on adjacent peatlands for water supply through hydraulic redistribution. Wildfire is common in the Boreal Plains, so the resilience of the transfer of water from peatlands to uplands through roots immediately following wildfire may have implications for aspen succession. The objective of this research was to characterize post‐fire peatland‐upland hydraulic connectivity and assess controls on aspen transpiration (as a measure of stress and productivity) among landscape topographic positions. In May 2011, a wildfire affected 90,000 ha of north central Alberta, including the Utikuma Region Study Area (URSA). Portions of an URSA glacio‐fluval outwash lake catchment were burned, which included forests and a small peatland. Within 1 year after the fire, aspen were found to be growing in both the interior and margins of this peatland. Across recovering land units, transpiration varied along a topographic gradient of upland midslope (0.42 mm hr^?1) > upland hilltop (0.29 mm hr^?1) > margin (0.23 mm hr^?1) > peatland (0.10 mm hr^?1); similar trends were observed with leaf area and stem heights. Although volumetric water content was below field capacity, P. tremuloides were sustained through roots present, likely before fire, in peatland margins through hydraulic redistribution. Evidence for this was observed through the analysis of oxygen (δ¹⁸O) and hydrogen (δ²H) isotopes where upland xylem and peat core signatures were ?10.0‰ and ?117.8‰ and ?9.2‰ and ?114.0‰, respectively. This research highlights the potential importance of hydraulic redistribution to forest sustainability and recovery, in which the continued delivery of water may result in the encroachment of aspen into peatlands. As such, we suggest that through altering ecosystem services, peatland margins following fire may be at risk to aspen colonization during succession.     

Evidence for variations in cryogenic extraction deuterium biases of plant xylem water across foundational northeastern US trees

Measurements of oxygen and hydrogen isotopes in plant xylem water (²H, ¹⁸O) have helped to redefine conceptual and numerical models of the hydrological cycle and understand how plants compete for subsurface water. Recent experiments have shown that Cryogenic Vacuum Extraction (CVE) of plant xylem water can result in a δ²H bias. We tested if CVE δ²H-biases varied significantly across seven foundational northeastern US forest trees with a series of tree core rehydration experiments. Our analysis demonstrated that CVE δ²H-biases were well predicted by sample gravimetric water content and varied significantly with tree species identity. We show that species-level δ²H-bias corrections can result in substantially different understandings of plant water uptake and transpiration versus uncorrected data or generic bias corrections. This research demonstrates an urgent need for the critical evaluation of CVE for plant water extraction. In the absence of a stronger understanding of CVE δ²H-biases, we recommend that xylem water δ²H observations should not be used in plant water uptake studies.     

MAROS: a decision support system for optimizing monitoring plans

The Monitoring and Remediation Optimization System (MAROS), a decision-support software, was developed to assist in formulating cost-effective ground water long-term monitoring plans. MAROS optimizes an existing ground water monitoring program using both temporal and spatial data analyses to determine the general monitoring system category and the locations and frequency of sampling for future compliance monitoring at the site. The objective of the MAROS optimization is to minimize monitoring locations in the sampling network and reduce sampling frequency without significant loss of information, ensuring adequate future characterization of the contaminant plume. The interpretive trend analysis approach recommends the general monitoring system category for a site based on plume stability and site-specific hydrogeologic information. Plume stability is characterized using primary lines of evidence (i.e., Mann-Kendall analysis and linear regression analysis) based on concentration trends, and secondary lines of evidence based on modeling results and empirical data. The sampling optimization approach, consisting of a two-dimensional spatial sampling reduction method (Delaunay method) and a temporal sampling analysis method (Modified CES method), provides detailed sampling location and frequency results. The Delaunay method is designed to identify and eliminate redundant sampling locations without causing significant information loss in characterizing the plume. The Modified CES method determines the optimal sampling frequency for a sampling location based on the direction, magnitude, and uncertainty in its concentration trend. MAROS addresses a variety of ground water contaminants (fuels, solvents, and metals), allows import of various data formats, and is designed for continual modification of long-term monitoring plans as the plume or site conditions change over time.     

The dynamical and liquid water structure of the small cumulus as determined from its environment

This paper examines the evidence for the model of a small cumulus cloud represented as a quasi static but turbulent entity, growing on the upshear side and decaying on the downshear side. While the air just outside the cloudy outline is, on average, stationary relative to the embedding airmass, there is a slight flow, upwards and forward as though the updraft has induced upward motion in the clear air outside the cloud, on the growing side. On the decaying side the motion is downwards and away from the cloud.This is a flow pattern which is not consistent with the air flowing around the cloud as it moves forward but it agrees well with the picture given. Decayed remnants of cloud are found throughout the air previously occupied by the cloud. The cloud outline moves through the embedding air at a velocity which is almost as large as the relative motion of the subcloud feeding airflow (which is almost free from internal wind shear in strong convection).The mixing of dry air from above the inversion yields the observed diluted liquid water content in small cumuli, if such mixing is allowed to proceed until the cloud density equals that of the surrounding air. Quantitative conditions relating the liquid water to inversion temperature and moisture changes, and to the stability of the environment are presented. The strong vertical mixing from the top of the cloud downwards is important to microphysical processes.     

Recession of Martian north polar cap: 1979–1980 Viking observations

The 1979–1980 regression curve for the north polar cap of Mars, determined from Viking orbiter images, is compared to Viking observations of the same season 1 (Martin) year earlier and to telescopic observations. Differences between the two years cannot unambigously be attributed to dynamical effects because of uncertainties introduced by limited longitudinal coverage.     

Radar and photoelectric observations of asteroid 2100 Ra-Shalom

Results of 13-cm-wavelength radar observations and V-filter photoelectric observations of Ra- Shalom during its 1981 Aug–Sep apparition are reported. The radar data yid detections of echoes in the same sense of circular polarization as transmitted (i.e., the SC sense) as well as in the opposite (OC) sense. The estimate of the ratio of SC to OC echo power, μ_c = 0.14 ± 0.02, indicates that most, but certainly not all, of the backscattering is due to single reflections from surface elements that are fairly smooth at decimeter scales. The value obtained for the OC radar cross section on Aug 26 (1.2 ± 0.3 km²) is about three times larger than those obtained on Aug 23, 24, and 25. The echo bandwidth appears to be within about 1.5 Hz of 5.0 Hz on each date. The photoelectric data suggest a value, P_syn = 19.79 hr, for the synodic rotation period, and yield a composite lightcurve with two pairs of extrema. Combining this value for P_syn with a firm lower bound (4 Hz) on the maximum echo bandwidth yields a lower bound of 1.4 km on the maximum distance between Ra-Shalom's spin axis and any point on its surface.     

An Arecibo follow-up study of seven pulsars discovered by Five-hundred-meter Aperture Spherical radio Telescope(FAST)

We present Arecibo 327 MHz confirmation and follow-up studies of seven new pulsars discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST).These pulsars are discovered in a pilot program of the Commensal Radio Astronomy FAST Survey (CRAFTS) with the ultra-widebandwidth commissioning receiver.Five of them are normal pulsars and two are extreme nulling slow pulsars.PSR J2111+2132’s dispersion measure (DM:78.5 pc cm~(-3)) is above the upper limits of the two Galactic free electron density models,NE2001 and YMW16,and PSR J2057+2133’s position is out of the Scutum-Crux Arm,making them uniquely useful for improving the Galactic free electron density model in their directions.We present a detailed single pulse analysis for the slow nulling pulsars.We show evidence that PSR J2323+1214’s main pulse component follows a non-Poisson distribution and marginal evidence for a sub-pulse-drift or recurrent period of 32.3±0.4 rotations from PSR J0539+0013.We discuss the implication of our finding to the pulsar radiation mechanism.     

Travel times for snowmelt-dominated headwater catchments: Influences of wetlands and forest harvesting,and linkages to stream water quality

The time it takes water to travel through a catchment, from when it enters as rain and snow to when it leaves as streamflow, may influence stream water quality and catchment sensitivity to environmental change. Most studies that estimate travel times do so for only a few, often rain-dominated, catchments in a region and use relatively short data records (<10 years). A better understanding of how catchment travel times vary across a landscape may help diagnose inter-catchment differences in water quality and response to environmental change. We used comprehensive and long-term observations from the Turkey Lakes Watershed Study in central Ontario to estimate water travel times for 12 snowmelt-dominated headwater catchments, three of which were impacted by forest harvesting. Chloride, a commonly used water tracer, was measured in streams, rain, snowfall and as dry atmospheric deposition over a 31 year period. These data were used with a lumped convolution integral approach to estimate mean water travel times. We explored relationships between travel times and catchment characteristics such as catchment area, slope angle, flowpath length, runoff ratio and wetland coverage, as well as the impact of harvesting. Travel time estimates were then used to compare differences in stream water quality between catchments. Our results show that mean travel times can be variable for small geographic areas and are related to catchment characteristics, in particular flowpath length and wetland cover. In addition, forest harvesting appeared to decrease mean travel times. Estimated mean travel times had complex relationships with water quality patterns. Results suggest that biogeochemical processes, particularly those present in wetlands, may have a greater influence on water quality than catchment travel times.