Earth's Deserts Research Articles

Improvement in Dust Storm Simulation by Considering Stone Coverage Effects for Stony Deserts in East Asia

AbstractApproximately 50% of the Earth's deserts are covered with stony surfaces, not dunes. The stony surfaces often block or diminish mineral dust aerosol emissions through area fraction and roughness element effects. Incorporating these stone coverage effects is crucial for climate and environmental modeling research. Based on our field observations, this study combined the stone coverage effects into a dust simulation model for East Asia using two regression formulas and some constants. The double regression scheme assumed that the stone roughness density could be derived from the coarse fragment fraction of the SoilGrids 2.0 data set. According to the data set, the stone coverage is higher in Western Mongolia and Dzungaria and lower in the Chinese Gobi Desert and the Loess Plateau. Consequently, the model reproduced fewer dust aerosols in the higher coverage areas and more in the lower coverage areas. This simulation result was consistent with the World Meteorological Organization's current weather reports and satellite aerosol observations. The improved model reproduced the diversity of soil erodibility and was well balanced in performance statistics. This study is the first successful investigation of stone coverage effects on dust storm simulation using a realistic stone coverage map to the authors' best knowledge.

Grain-scale computations of barchan dunes

Barchans are crescent-shaped dunes commonly found in diverse environments and scales: from the 10-cm-long barchans found under water to the 1-km-long barchans on Mars, passing by the 100-m-long dunes on Earth's deserts. Although ubiquitous in nature, there is a lack of grain-scale computations of the growth and evolution of those bedforms. In this paper, we investigate the values of grain properties (coefficients of sliding friction, rolling friction, and restitution) necessary to carry out numerical simulations of subaqueous barchans with CFD–DEM (computational fluid dynamics–discrete element method), and how the values of those coefficients change the barchan dynamics. We made use of LES (large eddy simulation) for the fluid, varied the coefficients of sliding friction, rolling friction, and restitution in the DEM, and compared the outputs with experiments. We show (i) for the case of glass spheres, the values of coefficients for correctly obtaining the dune morphology, timescales, trajectories of individual grains, and forces experienced by grains; (ii) the LES meshes allowing computations of bedload while capturing the main disturbances of the fluid flow; (iii) how different values of coefficients affect the morphology of barchans; and (iv) that spheres with higher coefficients of rolling friction can be used for simulating barchans consisting of angular grains. Our results represent a significant step for performing simulations that capture, at the same time, details of the fluid flow (large eddies) and grains' motion (individual particles).

Origin of the intense positive and moderate negative atmospheric electric field variations measured during and after Antarctic blizzards

There is an atmospheric electric field (AEF) or an electric potential gradient (PG) in fair weather between the Earth's surface and the mesosphere/ionosphere, which is positive. During blizzards/snowstorms in the polar regions, an intense positive AEF/PG in the order of 103 V/m of the same polarity in fair weather was observed using an electric field mill at 1.4 m in height. In contrast, a moderately negative AEF/PG variation after a blizzard was observed in 2015 at Syowa Station, Antarctica. The negative variation, where the magnitude ranged from tens to hundreds of V/m, gradually recovered into the positive AEF/PG for more than 40 min. According to various studies on blowing/drifting snow dynamics and electricity in laboratory experiments and field observations, snow particles colliding with the snow surface are charged, and the charge of suspended and saltating particles during the snowstorm is negative on average. To verify the AEF/PG observed during and after the blizzards, we numerically estimated the electric field surrounding the conductive sensor unit of the electric field mill using a three-dimensional Poisson equation. Under blizzard conditions, the polarity of the estimated AEF/PG was the opposite of that of the observed AEF/PG. From the noise study of the field mill, we deduced that the positive AEF/PG variations were caused by the collision of negatively charged snow particles with the electric probe on the sensor unit. Just after the blizzard, the number of snow particles measured at 4.4 m in height clearly decreased, and the camera image showed clear visibility. From this evidence, we modeled the suspended and saltating negatively charged snow particles that had fallen onto the ground surface and then constructed a charge layer of the snow particles softly attaching to the ground, which slowly discharged following the study on the electrical resistance of the powders. The three-dimensional Poisson calculation based on the model reproduced a moderately negative AEF/PG. Thus, we elucidated that the origins of the intense positive and moderate negative electric fields during and after blizzards are the charged snow particles colliding with the electric probe on the sensor unit and the negative snow layers softly attached to the ground, respectively. These results are applicable to studies on dust storm electrification on Mars' and Earth's deserts, snowstorm electrification in the polar regions, and high mountains, such as Mt. Fuji in Japan, and turbulent electrification for industrial dust, which provides the identification of intense electrification and storms.

The EMIT mission information yield for mineral dust radiative forcing

The net direct radiative effect of mineral dust is a large uncertainty in global radiative forcing. To address this challenge, NASA's Earth Mineral dust source InvesTigation (EMIT) will map the surface mineralogy of Earth's desert dust source regions, constraining the composition of mineral dust aerosol for use in Earth system models (ESMs). This mission foreshadows multiple future global spectroscopic investigations for which coupling with ESMs will play a critical role. Planning such experiments requires a methodology for assessing the impact of uncertain remote observations on ESM accuracy. We design and implement an end-to-end simulation of the EMIT mission, leveraging Bayesian statistical methods and Monte Carlo sampling to analyze uncertainties in the retrieval and processing of EMIT data products. Special focus is placed on those uncertainties caused by atmospheric water vapor and aerosol loading conditions likely to be encountered by EMIT. We apply these results to a single-column configuration of the Community Earth System Model (CESM), revealing the potential impact of EMIT observations on radiative forcing estimates. We show that EMIT data stand to significantly reduce uncertainty in estimates of the dust direct radiative forcing attributable to uncertainties in surface mineralogies that are input to ESMs, and that the information gain for radiative forcing comes predominantly from better constraining iron oxides, which dominate the shortwave radiative effects of aerosol dust.

Nitrate, perchlorate, and iodate co-occur in coastal and inland deserts on Earth

Deserts accumulate soluble salts from atmospheric deposition that impact human health, are a source of nutrients for organisms, and provide insight into how landscapes evolved on Earth and Mars. We quantified perchlorate, nitrate, and iodate abundances and co-occurrence in terrestrial deserts to identify fundamental controls on soluble salt deposition and post-depositional cycling. Soils and nitrate deposits were examined in Death Valley, USA; Atacama Desert, Chile; Kumtag Desert, China; and along an environmental gradient in the Transantarctic Mountains, Antarctica. Concentrations of soluble salts were highest in the Transantarctic Mountains and Atacama Desert, where stable, hyper-arid landscapes accumulate atmospheric salts over million-year time scales. Average nitrate concentrations of 61.3gkg−1 in the Transantarctic Mountains and 53.0gkg−1 in the Atacama Desert were significantly greater than respective averages of 8.60gkg−1 and 5.14gkg−1 in Kumtag Desert and Death Valley. Perchlorate and iodate concentrations in the Atacama Desert averaged 206mgkg−1 and 344mgkg−1, respectively, which were two to three orders of magnitude greater than in Antarctica and other sites. Our findings suggest that local processes in the Atacama Desert result either in higher rates of perchlorate and iodate deposition, or a greater preservation of these salts relative to nitrate when compared to Antarctic landscapes. Lower salt concentrations in the Death Valley and Kumtag Desert deposits likely result from relatively wet present-day and paleoclimatic conditions, a more active geologic history, and a greater likelihood that biocycling disrupted long-term salt accumulation. Associations of perchlorate and nitrate were significantly higher than iodate-nitrate and iodate-perchlorate correlations in the four deserts. Perchlorate-nitrate relationships ranged from insignificant to highly significant with stronger correlations in the Atacama Desert and Kumtag Desert compared to the Transantarctic Mountains and Death Valley. Weaker geochemical associations with iodate were attributed to differences in local deposition rates or post-depositional cycling. Interestingly, relationships among perchlorate, nitrate, and iodate were generally stronger when examined by site within each desert compared to analyzing the soils for each desert as a whole, suggesting more localized controls on soluble salt preservation. We conclude that soluble salts vary in concentration and type across Earth's deserts as a result of present-day environment, paleoclimate conditions, biocycling, and geologic age.

Hyperarid Soils and the Soil Taxonomy

In the past decade, pedological research in hyperarid environments worldwide has revealed landscapes and soil features that are regionally prevalent and distinctive, but not well captured in the current soil taxonomy. Hyperarid soils bear genetic features that can differ considerably from those in more humid desert environments. In particular, they often contain horizons cemented with halite (NaCl) or heavily enriched with nitratine (NaNO3). Unlike soils commonly found in more humid regions, they may also lack most vascular plants, pedogenic carbonates, and biotic mixing processes. Based on the global occurrence of indurated salic horizons and nitric horizons in hyperarid soils, we propose that the soil taxonomy be amended to include a petrosalic diagnostic subsurface horizon, a nitric diagnostic subsurface horizon, and Petrosalids great group within the Aridisols order. Additionally, we suggest the definition and establishment of a Hyperaridic Soil Moisture Regime (SMR). In this paper, we use soils from the Atacama Desert to illustrate how pedogenesis in extreme hyperarid environments differs from that in more humid environments, and we review the current literature regarding soils in other hyperarid locations with indurated soluble salt horizons. The changes proposed here would create a more encompassing classification system for the Earth's desert regions, improving our ability to clearly communicate relevant genetic, ecological, and economic information to both land‐managers and researchers.

Dynamic cyanobacterial response to hydration and dehydration in a desert biological soil crust

Biological soil crusts (BSCs) cover extensive portions of the earth's deserts. In order to survive desiccation cycles and utilize short periods of activity during infrequent precipitation, crust microorganisms must rely on the unique capabilities of vegetative cells to enter a dormant state and be poised for rapid resuscitation upon wetting. To elucidate the key events involved in the exit from dormancy, we performed a wetting experiment of a BSC and followed the response of the dominant cyanobacterium, Microcoleus vaginatus, in situ using a whole-genome transcriptional time course that included two diel cycles. Immediate, but transient, induction of DNA repair and regulatory genes signaled the hydration event. Recovery of photosynthesis occurred within 1 h, accompanied by upregulation of anabolic pathways. Onset of desiccation was characterized by the induction of genes for oxidative and photo-oxidative stress responses, osmotic stress response and the synthesis of C and N storage polymers. Early expression of genes for the production of exopolysaccharides, additional storage molecules and genes for membrane unsaturation occurred before drying and hints at preparedness for desiccation. We also observed signatures of preparation for future precipitation, notably the expression of genes for anaplerotic reactions in drying crusts, and the stable maintenance of mRNA through dormancy. These data shed light on possible synchronization between this cyanobacterium and its environment, and provides key mechanistic insights into its metabolism in situ that may be used to predict its response to climate, and or, land-use driven perturbations.

A new concept for the global distribution of solar energy: energy carrying compounds

A new concept for storage and superregional transport of solar energy from the earth's desert belt is proposed. The concept is based on solid alkaline earth metal compounds, showing an energy-rich and an energy-lean state which are used in an energy distribution cycle. The concept is evaluated with regard to overall solar-to-electricity efficiency and benchmarked by the overall efficiency of the DESERTEC concept. For a scenario assuming that the current share of electricity production from lignite coal in Germany is replaced by the here proposed concept, the CO2 mitigation potential is calculated. The assessment shows that the proposed concept can compete with the benchmark and even shows high potential for optimization.

Control of the Aero‐Electric Power Station—an exciting QFT application for the 21st century

AbstractThe Aero‐Electric Power Station is the ultimate solar power station, utilizing the dry, hot air of Earth's desert zones. By spraying water at the top of e.g. a 1200 m tall chimney with a diameter of 400 m, the air is cooled by evaporation and flows downwards through turbines at the bottom, generating 380 MW of net electric power. The Aero‐Electric Power Station is still in the planning stage, and this paper belongs to a long series of feasibility studies.The current ‘truth’ model of the Aero‐Electric Power Station is a one‐dimensional partial differential equation model. The external slowly changing weather, defined as the mean air pressures, temperatures and humidity at the top and bottom of the tower, determines the optimal operating point, i.e. the optimal water spray flow and turbine velocity that give the largest net power. The gross power produced by the turbine is partly delivered to the grid and partly to pump sea water to spray water reservoirs. The reservoirs make it possible to use the pumping power and the spray flow rate as control.Wind changes cause significant deviations from the mean external air pressures, requiring closed loop regulation to keep the rotor velocity constant. The Aero‐Electric Power Station may be modelled as an uncertain, unstable irrational transfer function, with two disturbances (external air pressure deviations at top and bottom), two control variables (turbine power and spray flow), and one output (rotor velocity), without a cascaded structure, giving rise to a robust load sharing control problem.A robust linear feedback regulator is designed by QFT, in such a way that the load of regulation is shared between the two control inputs. A closed loop step response simulation for one operating condition, using the ‘truth’ model, demonstrates the design. Copyright © 2003 John Wiley & Sons, Ltd.

New insights into Martian dust distribution and water‐ice cloud microphysics

In this paper we use a direct method which combines microphysics and photometric simulations of the Martian atmosphere. This approach allows us to reproduce vertical profiles of the light scattered by the haze at the limb of Mars. Subsequent results are compared to a multiple‐color image provided by the Viking Orbiter camera. The “free parameters” of our study are related to vertical transport and dust size distribution. A sensitivity study has been conducted, encompassing a relevant range of parameters, in order to obtain the most satisfying multispectral modeled profile with respect to the one inferred from data. Except for an unlikely distribution of submicron particles (reff ∼ 0.2 μm), no consistent fit can be obtained. This implies that size distributions of dust suggested by previous studies are not in agreement with the present analysis. This apparent discrepancy can be resolved by adding a separate peak of submicron particles to the size distribution previously extracted from Viking Lander images. Only in that case can spectral and vertical structures of haze be successfully matched. While a bimodal distribution would change the current picture of Martian dust, such distribution is a common representation of soil‐derived aerosol size function in Earth deserts. We also attempted to derive information from the cloud shown in the Viking limb image. Our estimates suggest that cloud particle effective radius is around 1.2–1.8 μm, while the cloud visible opacity is 0.02.

Respiratory physiology of birds: Considerations for anesthetic management

As veterinarians, we are indeed fortunate to be able to work with animals from a variety of taxonomic groups. The anatomic and physiological differences among animal taxa affect how we manage these animals. Anatomic differences are obvious, but it is the subtle differences in physiological function that challenge our knowledge and experience. The unique anatomy and physiology of birds enable some to fly at altitudes of 32,000 feet without supplemental oxygen, to dive underwater for many minutes, and to live at environmental extremes from the frozen deserts of the polar caps, to the heat and humidity of the tropics, to the dry heat of the earth's deserts. This article reviews unique anatomic and physiological features of the avian respiratory system, and how they impact on anesthetic management.

Jovian desert and light show

The water content of Jupiter varies at least as much as moisture varies between Earth's deserts and rainforests, according to new images and data from the Galileo spacecraft. That variation might explain why Galileo's atmospheric probe found less water than expected when it was dropped into the Jovian atmosphere in December 1995. Members of the Galileo science team suspected that the probe landed in the “Sahara Desert of Jupiter.”

The effect on regional and global climate of expansion of the world's deserts

An atmospheric general-circulation model with realistic land-surface properties is used to investigate the climatic effect of doubling the extent of the earth's deserts. Control and anomaly integrations are performed for 10 years. In the anomaly case, deserts are expanded over northern and southern Africa, Australia, south-central Asia, south-western North America, and parts of South America. In the anomaly case, the troposphere is cooler across most of the tropics and subtropics, including all areas where desertification occurs. Remote effects in the winter circulation include a pronounced trough over northern Europe, and increased geopotential heights over the southern oceans. The response of climate in deforested areas is not uniform between the regions. The magnitude and seasonality of the changes, particularly in precipitation, seem to be functions of the monsoon regime. Northern Africa suffers a strong year-round drought, suggesting this area is most sensitive to desertification, and southern Africa has a somewhat weaker year-round drought. Rainfall over desertified parts of Asia, Australia and western South America decreases only during the summer, and not during the winter. North America and the Nordeste region of Brazil show the least sensitivity to desertification. Most regions show a notable correlation between decreases in evapotranspiration and resulting precipitation. However, regional land–sea distributions in the vicinity of each desertified area appear to determine the sensitivity and response of the local climate via induced changes in moisture flux convergence. Thus, different regions exhibit different responses of climate to desertification. Surface temperature decreases over most desertified areas, owing to reduced absorption of short-wave radiation by the brighter surface. Some regions, particularly the Sahel, show an increase in surface temperature caused by decreased soil moisture and latent-heat flux.

The effect on regional and global climate of expansion of the world's deserts

AbstractAn atmospheric general‐circulation model with realistic land‐surface properties is used to investigate the climatic effect of doubling the extent of the earth's deserts. Control and anomaly integrations are performed for 10 years. In the anomaly case, deserts are expanded over northern and southern Africa, Australia, south‐central Asia, south‐western North America, and parts of South America.In the anomaly case, the troposphere is cooler across most of the tropics and subtropics, including all areas where desertification occurs. Remote effects in the winter circulation include a pronounced trough over northern Europe, and increased geopotential heights over the southern oceans. The response of climate in deforested areas is not uniform between the regions. The magnitude and seasonality of the changes, particularly in precipitation, seem to be functions of the monsoon regime. Northern Africa suffers a strong year‐round drought, suggesting this area is most sensitive to desertification, and southern Africa has a somewhat weaker year‐round drought. Rainfall over desertified parts of Asia, Australia and western South America decreases only during the summer, and not during the winter. North America and the Nordeste region of Brazil show the least sensitivity to desertification. Most regions show a notable correlation between decreases in evapotranspiration and resulting precipitation. However, regional land–sea distributions in the vicinity of each desertified area appear to determine the sensitivity and response of the local climate via induced changes in moisture flux convergence. Thus, different regions exhibit different responses of climate to desertification. Surface temperature decreases over most desertified areas, owing to reduced absorption of short‐wave radiation by the brighter surface. Some regions, particularly the Sahel, show an increase in surface temperature caused by decreased soil moisture and latent‐heat flux.

Nitrogen photoreduction on desert sands under sterile conditions

Sands from various geographic locations reduce N(2) from the air to NH(3) and traces of N(2)H(4) on exposure to sunlight. This N(2) photofixation occurs under sterile conditions on the surface of finely dispersed titanium minerals such as rutile, utilizing reducing equivalents generated through the photolysis of chemisorbed H(2)O. Abiological N(2) photofixation is suggested to be part of the nitrogen cycle in arid and semiarid regions. It is estimated that about 10 x 10(5) tons of N(2) is photoreduced on the total surface of the earth's deserts per year.

Connections Between Climate and Desertification

The widespread fear that the Earth's deserts are spreading was reawakened by the major 1968–73 drought in Sahelian West Africa, Sudan, Ethiopia, and parts of Kenya. There appears, however, to be no firm evidence that a permanent desiccation of the arid zone is in progress. Instead, the evidence suggests that ‘desertification’—defined as the spread of desert surfaces, regardless of cause—results more immediately from faulty land-use practices and their interaction with prolonged natural drought episodes.Desertification appears to be a process of degradation of grassland, scrub, or savanna, ecosystems under the impact of overstocking or excessive cultivation. During periods of desiccation there is widespread destruction of perennial vegetation, compaction of soil (especially near watering places), and deflation of fine materials (wind erosion).Such surfaces are lighter-coloured than native vegetation, and reflect more sunlight. This may enhance atmospheric subsidence, and hence intensify drought. Loss of surface organic litter may also act as a positive feedback for drought.Prediction of such episodes is at least some years away, but three possibilities exist for such prediction: use of cyclical variations, where present; time-lagged teleconnections; and general circulation modelling.Reduced infiltration in some arid areas, combined with excessive withdrawals in others, have lowered both shallow alluvial and deep fossil ground-water tables—in some areas to the point at which stock water-supply can no longer be maintained.