Airborne particles of mineral dust play a key role in Earth's climate system
and affect human activities around the globe. The numerical weather modeling
community has undertaken considerable efforts ...to accurately forecast these
dust emissions. Here, for the first time in the literature, we thoroughly
describe and document the Air Force Weather Agency (AFWA) dust emission
scheme for the Georgia Institute of Technology–Goddard Global Ozone
Chemistry Aerosol Radiation and Transport (GOCART) aerosol model within the Weather Research and
Forecasting model with chemistry (WRF-Chem) and compare it to the other dust
emission schemes available in WRF-Chem. The AFWA dust emission scheme
addresses some shortcomings experienced by the earlier GOCART-WRF scheme.
Improved model physics are designed to better handle emission of fine dust
particles by representing saltation bombardment. WRF-Chem model performance
with the AFWA scheme is evaluated against observations of dust emission in
southwest Asia and compared to emissions predicted by the other schemes built
into the WRF-Chem GOCART model. Results highlight the relative strengths of
the available schemes, indicate the reasons for disagreement, and demonstrate
the need for improved soil source data.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Abstract
Blowing snow presents substantial risk to human activities by causing severe visibility degradation and snow drifting. Furthermore, blowing snow presents a weather forecast challenge since ...it is not generally simulated in operational weather forecast models. In this study, we apply a physically based blowing snow model as a diagnostic overlay to output from a reforecast WRF simulation of a significant blowing snow event that occurred over the northern Great Plains of the United States during the winter of 2019. The blowing snow model is coupled to an optics parameterization that estimates the visibility reduction by blowing snow. This overlay is qualitatively evaluated against false color satellite imagery from the
GOES-16
operational weather satellite and available surface visibility observations. The WRF-simulated visibility is substantially improved when incorporating blowing snow hydrometeors. Furthermore, the model-simulated plume of blowing snow roughly corresponds to the blowing snow plumes visible in the satellite imagery. Overall, this study illustrates how a blowing snow diagnostic model can aid weather forecasters in making blowing snow visibility forecasts, and demonstrates how the model can be evaluated against satellite imagery.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Roughness features (e.g., rocks, vegetation, furrows) that shelter or attenuate wind flow over the soil surface can considerably affect the magnitude and spatial distribution of sediment transport in ...active aeolian environments. Existing dust and sediment transport models often rely on vegetation attributes derived from static land use datasets or remotely sensed greenness indicators to incorporate sheltering effects on simulated particle mobilization. However, these overly simplistic approaches do not represent the three-dimensional nature or spatiotemporal changes of roughness element sheltering. They also ignore the sheltering contribution of non-vegetation roughness features and photosynthetically inactive (i.e., brown) vegetation common to dryland environments. Here, we explore the use of a novel albedo-based sheltering parameterization in a dust transport modeling application of the Weather Research and Forecasting model with Chemistry (WRF-Chem). The albedo method estimates sheltering effects on surface wind friction speeds and dust entrainment from the shadows cast by subgrid-scale roughness elements. For this study, we applied the albedo-derived drag partition to the Air Force Weather Agency (AFWA) dust emission module and conducted a sensitivity study on simulated PM10 concentrations using the Georgia Institute of Technology–Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model as implemented in WRF-Chem v4.1. Our analysis focused on a convective dust event case study from 3–4 July 2014 for the southwestern United States desert region discussed by other published works. Previous studies have found that WRF-Chem simulations grossly overestimated the dust transport associated with this event. Our results show that removing the default erodibility map and adding the drag parameterization to the AFWA dust module markedly improved the overall magnitude and spatial pattern of simulated dust conditions for this event. Simulated PM10 values near the leading edge of the storm substantially decreased in magnitude (e.g., maximum PM10 values were reduced from 17 151 to 8539 µg m−3), bringing the simulated results into alignment with the observed PM10 measurements. Furthermore, the addition of the drag partition restricted the erroneous widespread dust emission of the original model configuration. We also show that similar model improvements can be achieved by replacing the wind friction speed parameter in the original dust emission module with globally scaled surface wind speeds, suggesting that a well-tuned constant could be used as a substitute for the albedo-based product for short-duration simulations in which surface roughness is not expected to change and for landscapes wherein roughness is constant over years to months. Though this alternative scaling method requires less processing, knowing how to best tune the model winds a priori could be a considerable challenge. Overall, our results demonstrate how dust transport simulation and forecasting with the AFWA dust module can be improved in vegetated drylands by calculating the dust emission flux with surface wind friction speed from a drag partition treatment.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Obtaining reliable estimates of aerodynamic roughness is necessary to interpret and accurately predict aeolian sediment transport dynamics. However, inherent uncertainties in field measurements and ...models of surface aerodynamic properties continue to undermine aeolian research, monitoring, and dust modeling. A new relation between aerodynamic shelter and land surface shadow has been established at the wind tunnel scale, enabling the potential for estimates of wind erosion and dust emission to be obtained across scales from albedo data. Here, we compare estimates of wind friction velocity (u*) derived from traditional methods (wind speed profiles) with those derived from the albedo model at two separate scales using bare soil patch (via net radiometers) and landscape (via Moderate Resolution Imaging Spectroradiometer MODIS 500 m) data sets. Results show that profile‐derived estimates of u* are highly variable in anisotropic surface roughness due to changes in wind direction and fetch. Wind speed profiles poorly estimate soil surface (bed) wind friction velocities necessary for aeolian sediment transport research and modeling. Albedo‐based estimates of u* at both scales have small variability because the estimate is integrated over a defined, fixed area and resolves the partition of wind momentum between roughness elements and the soil surface. We demonstrate that the wind tunnel‐based calibration of albedo for predicting wind friction velocities at the soil surface (us*) is applicable across scales. The albedo‐based approach enables consistent and reliable drag partition correction across scales for model and field estimates of us* necessary for wind erosion and dust emission modeling.
Key Points
First field test of albedo approach to estimate total and surface friction velocities over a rough bed
Albedo‐derived estimates of total friction velocity were consistent with friction velocities obtained from wind speed profiles
Field measurements of surface wind friction velocities consistent with wind tunnel data, confirming the albedo approach is scale invariant
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Controls on the particle size distribution (PSD) of mineral dust emissions remain poorly understood. Under near‐idealized conditions, dust PSDs can appear invariant with wind friction velocity. ...However, dryland vegetation attenuates surface friction velocities, and soil crusting reduces the supply of loose erodible material and increases surface resistance to abrasion. Under such conditions, variability in saltation bombardment efficiency and intensity could have a large effect on dust PSDs. We present dust emission measurements from vegetated, supply‐limited aeolian systems that indicate the dependence of emission‐flux PSD on wind friction velocity. We find the fine fraction (<5 μm) of dust particles increases with friction velocity. Results suggest models that assume wind‐invariance of the emission‐flux PSD may not be generalizable for crusted soils with vegetation. There is a need for dust models to represent variability in emission‐flux PSDs for land management, air quality, and climate applications across vegetated and sediment supply‐limited drylands.
Plain Language Summary
The size of dust particles emitted into the air during wind erosion determines how soils are affected and how dust influences air quality and climate. However, much remains unknown about how wind speed, soil properties, and vegetation influence the size of emitted dust at different locations. Some studies suggest that when land is unvegetated and soils are loose, the size of emitted dust does not change with wind speed. We measured the size of dust emitted from vegetated landscapes with soils that are crusted and have changing amounts of loose erodible sediment. We found that wind speed has a strong effect on the size of emitted dust particles. Stronger winds produced finer dust at sites with weaker soil crusts and more loose erodible sediment. Predictive models need to consider the changing size of emitted dust particles in different environments in order to more accurately assess wind erosion and dust impacts.
Key Points
Dust emission flux particle size distribution is dependent on wind friction velocity over vegetated and crusted dryland soils
Dust emission flux is enriched in fine (<5 μm) particles with increasing wind friction velocity
Dust emission models need to represent variability in dust particle size distribution from sediment supply‐limited aeolian systems
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Dust transported from rangelands of the Southwestern United States (US) to mountain snowpack in the Upper Colorado River Basin during spring (March‐May) forces earlier and faster snowmelt, which ...creates problems for water resources and agriculture. To better understand the drivers of dust events, we investigated large‐scale meteorology responsible for organizing two Southwest US dust events from two different dominant geographic locations: (a) the Colorado Plateau and (b) the northern Chihuahuan Desert. High‐resolution Weather Research and Forecasting coupled with Chemistry model (WRF‐Chem) simulations with the Air Force Weather Agency dust emission scheme incorporating a MODIS albedo‐based drag‐partition was used to explore land surface‐atmosphere interactions driving two dust events. We identified commonalities in their meteorological setups. The meteorological analyses revealed that Polar and Sub‐tropical jet stream interaction was a common upper‐level meteorological feature before each of the two dust events. When the two jet streams merged, a strong northeast‐directed pressure gradient upstream and over the source areas resulted in strong near‐surface winds, which lifted available dust into the atmosphere. Concurrently, a strong mid‐tropospheric flow developed over the dust source areas, which transported dust to the San Juan Mountains and southern Colorado snowpack. The WRF‐Chem simulations reproduced both dust events, indicating that the simulations represented the dust sources that contributed to dust‐on‐snow events reasonably well. The representativeness of the simulated dust emission and transport in different geographic and meteorological conditions with our use of albedo‐based drag partition provides a basis for additional dust‐on‐snow simulations to assess the hydrologic impact in the Southwest US.
Plain Language Summary
Dust transported from rangelands of the Southwestern United States (US) to the mountain snowpack in the Upper Colorado River Basin during spring (March–May) is a growing problem for water resources and agriculture. Understanding the drivers of dust events is essential to better forecast the possible impact of dust on water resources. We investigated the weather conditions that led to two dust events originating from the Colorado Plateau and northern Chihuahuan Desert. We also performed computer simulations with an improved dust emission model to explore the influence of vegetation on the susceptibility of landscapes to wind erosion during dust events. Our meteorological analysis revealed commonalities in the upper‐level meteorology before dust event formation and provided valuable insights into where and when high‐impact dust events may occur. However, further investigation is needed to generalize the impact of jet stream interaction on dust events' intensity. Our simulations represented the dust sources reasonably well by using an improved dust emission model. The improved dust emission and transport simulation under different meteorological and geographical conditions provided a basis for future dust‐on‐snow simulations to assess the hydrological impact in the Southwestern US.
Key Points
Large‐scale meteorological analysis and dust emission and transport simulation of Southwest US dust‐on‐snow events
Polar and Sub‐tropical jet stream interaction was a common upper‐level meteorological feature to Southwest US dust events
Simulated dust source areas on the Colorado Plateau and Chihuahuan Desert reflect observed dust emission hot spots
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•Drag partition schemes have been applied to adjust the threshold friction velocity.•The applications have been incomplete and overestimate aeolian transport.•Corrections for ground cover can ...constitute double-accounting of erodible area.
Sediment transport equations used in wind erosion and dust emission models generally incorporate a threshold for particle motion (u*t) with a correction function to account for roughness-induced momentum reduction and aerodynamic sheltering. The prevailing approach is to adjust u*t by the drag partition R, estimated as the ratio of the bare soil threshold (u*ts) to that of the surface in the presence of roughness elements (u*tr). Here, we show that application of R to adjust only the entrainment threshold (u*t = u*ts/R) is physically inconsistent with the effect of roughness on the momentum partition as represented in models and produces overestimates of the sediment flux density (Q). Equations for Q typically include a friction velocity scaling term (u*n). As Q scales with friction velocity at the soil surface (us*), rather than total friction velocity (u*) acting over the roughness layer, u*n must be also adjusted for roughness effects. Modelling aeolian transport as a function of us* represents a different way of thinking about the application of some drag partition schemes but is consistent with understanding of aeolian transport physics. We further note that the practice of reducing Q by the vegetation cover fraction to account for the physically-protected surface area constitutes double accounting of the surface protection when R is represented through the basal-to-frontal area ratio of roughness elements (σ) and roughness density (λ). If the drag partition is implemented fully, additional adjustment for surface protection is unnecessary to produce more accurate aeolian transport estimates. These findings apply equally to models of the vertical dust flux.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Toxoplasma gondii belongs to the Apicomplexa phylum, which comprises protozoan parasites of medical and veterinary significance, responsible for a wide variety of diseases in human and animals, ...including malaria, toxoplasmosis, coccidiosis and cryptosporidiosis. During infection in the intermediate host,
T. gondii undergoes stage conversion between the rapidly replicating tachyzoite that is responsible for acute toxoplasmosis and the dormant or slowly dividing encysted bradyzoite. The tachyzoite–bradyzoite interconversion is central to the pathogenic process and is associated with the life-threatening recrudescence of infection observed in immunocompromised patients such as those suffering from AIDS. In chronic infections, the bradyzoites are located within tissue cysts found predominantly in brain and muscles. The tissue cyst is enclosed by a wall containing specific lectin binding sugars while the bradyzoites have accumulated large amounts of the storage polysaccharide of glucose, amylopectin. Our recent findings have identified several genes and proteins associated with amylopectin synthesis or degradation and glucose metabolism, including different isoforms of certain glycolytic enzymes, which are stage-specifically expressed during tachyzoite–bradyzoite interconversion. Here, we will discuss how the genes and enzymes involved in carbohydrate metabolisms are used as molecular and biochemical tools for the elucidation of molecular mechanisms controlling
T. gondii stage interconversion and cyst formation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Four analysts mapped dust sources using a modified Walker et al. (2009) method.•Walker et al. (2009) imply the method yields <10 km in dust source location error.•Our results suggest this estimate ...should be increased due to analyst subjectivity.•<10% of all dust sources were mapped by all participating analysts.•Walker et al. (2009) method dust source maps may vary substantially between users.
Accurate dust-source characterizations are critical for effectively modeling dust storms. A previous study developed an approach to manually map dust plume-head point sources in a geographic information system (GIS) framework using Moderate Resolution Imaging Spectroradiometer (MODIS) imagery processed through dust-enhancement algorithms. With this technique, the location of a dust source is digitized and recorded if an analyst observes an unobscured plume head in the imagery. Because airborne dust must be sufficiently elevated for overland dust-enhancement algorithms to work, this technique may include up to 10 km in digitized dust-source location error due to downwind advection. However, the potential for error in this method due to analyst subjectivity has never been formally quantified. In this study, we evaluate a version of the methodology adapted to better enable reproducibility assessments amongst multiple analysts to determine the role of analyst subjectivity on recorded dust source location error. Four analysts individually mapped dust plumes in Southwest Asia and Northwest Africa using five years of MODIS imagery collected from 15 May to 31 August. A plume-source location is considered reproducible if the maximum distance between the analyst point-source markers for a single plume is ≤10 km. Results suggest analyst marker placement is reproducible; however, additional analyst subjectivity-induced error (7 km determined in this study) should be considered to fully characterize locational uncertainty. Additionally, most of the identified plume heads (>90%) were not marked by all participating analysts, which indicates dust source maps generated using this technique may differ substantially between users.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Honey mesquite green-up increased aerodynamic drag partitioning and surface sheltering.•Magnitude and variability of surface shear velocity decreased following green-up.•Changes in the drag ...partition were driven by changes in foliar cover.•Representing plant phenology in drag partition could improve dust model accuracy.
Accurate representation of surface roughness in predictive models of aeolian sediment transport and dust emission is required for model accuracy and for models to inform wind erosion management. While past wind tunnel and field studies have examined roughness effects on drag partitioning, the spatial and temporal variability of surface shear velocity and the shear stress ratio remain poorly described. Here, we use a four-month dataset of total shear velocity (u*) and soil surface shear velocity (us*) measurements to examine the spatiotemporal variability of the shear stress ratio (R) before, during, and after vegetation green-up at a honey mesquite (Prosopis glandulosa Torr.) shrub-invaded grassland in the Chihuahuan Desert, New Mexico, USA. Results show that vegetation green-up, the emergence of leaves, led to increased drag and surface aerodynamic sheltering and a reduction in us* and R magnitude and variability. We found that us* decreased from 20% to 5% of u* as the vegetation form drag and its sheltering effect increased. Similarly, the spatiotemporal variability of R was found to be linked directly to plant phenological phases. We conclude that drag partition schemes should incorporate seasonal vegetation change, via dynamic drag coefficients and/or R, to accurately predict the timing and magnitude of seasonal aeolian sediment fluxes. The drag partition response to mesquite phenological phases also provided insight to potential mesquite herbicide treatment effects which, if successful, could increase wind erosivity and the onsite and downwind impacts of wind erosion unless protection by herbaceous plants is maintained.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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