2,567 research outputs found
The physics of wind-blown sand and dust
The transport of sand and dust by wind is a potent erosional force, creates
sand dunes and ripples, and loads the atmosphere with suspended dust aerosols.
This article presents an extensive review of the physics of wind-blown sand and
dust on Earth and Mars. Specifically, we review the physics of aeolian
saltation, the formation and development of sand dunes and ripples, the physics
of dust aerosol emission, the weather phenomena that trigger dust storms, and
the lifting of dust by dust devils and other small-scale vortices. We also
discuss the physics of wind-blown sand and dune formation on Venus and Titan.Comment: 72 journal pagers, 49 figure
Evaluation of a Potential for Enhancing the Decision Support System of the Interagency Modeling and Atmospheric Assessment Center with NASA Earth Science Research Results
NASA's objective for the Applied Sciences Program of the Science Mission Directorate is to expand and accelerate the realization of economic and societal benefits from Earth science, information, and technology. This objective is accomplished by using a systems approach to facilitate the incorporation of Earth observations and predictions into the decision-support tools used by partner organizations to provide essential services to society. The services include management of forest fires, coastal zones, agriculture, weather prediction, hazard mitigation, aviation safety, and homeland security. In this way, NASA's long-term research programs yield near-term, practical benefits to society. The Applied Sciences Program relies heavily on forging partnerships with other Federal agencies to accomplish its objectives. NASA chooses to partner with agencies that have existing connections with end-users, information infrastructure already in place, and decision support systems that can be enhanced by the Earth science information that NASA is uniquely poised to provide (NASA, 2004)
New developments in the representation of Saharan dust sources in the aerosol–climate model ECHAM6-HAM2
In the aerosol–climate model ECHAM6-HAM2, dust source activation (DSA)
observations from Meteosat Second Generation (MSG) satellite are proposed to
replace the original source area parameterization over the Sahara Desert.
The new setup is tested in nudged simulations for the period 2007 to 2008.
The evaluation is based on comparisons to dust emission events inferred from
MSG dust index imagery, Aerosol Robotic Network (AERONET) sun photometer observations, and satellite
retrievals of aerosol optical thickness (AOT).<br><br>The model results agree well with AERONET measurements especially in terms
of seasonal variability, and a good spatial correlation was found between
model results and MSG-SEVIRI (Spinning-Enhanced Visible and InfraRed Imager) dust AOT as well as Multi-angle Imaging SpectroRadiometer (MISR) AOT. ECHAM6-HAM2 computes a more realistic
geographical distribution and up to 20 % higher annual Saharan dust
emissions, using the MSG-based source map. The representation of dust AOT is
partly improved in the southern Sahara and Sahel. In addition, the spatial
variability is increased towards a better agreement with observations
depending on the season. Thus, using the MSG DSA map can help to circumvent
the issue of uncertain soil input parameters.<br><br>An important issue remains the need to improve the model representation of
moist convection and stable nighttime conditions. Compared to sub-daily DSA
information from MSG-SEVIRI and results from a regional model, ECHAM6-HAM2
notably underestimates the important fraction of morning dust events by the
breakdown of the nocturnal low-level jet, while a major contribution is from
afternoon-to-evening emissions
Impact of Surface Roughness and Soil Texture on Mineral Dust Emission Fluxes Modeling
Dust production models (DPM) used to estimate vertical fluxes of mineral dust aerosols over arid regions need accurate data on soil and surface properties. The Laboratoire Inter-Universitaire des Systemes Atmospheriques (LISA) data set was developed for Northern Africa, the Middle East, and East Asia. This regional data set was built through dedicated field campaigns and include, among others, the aerodynamic roughness length, the smooth roughness length of the erodible fraction of the surface, and the dry (undisturbed) soil size distribution. Recently, satellite-derived roughness length and high-resolution soil texture data sets at the global scale have emerged and provide the opportunity for the use of advanced schemes in global models. This paper analyzes the behavior of the ERS satellite-derived global roughness length and the State Soil Geographic data base-Food and Agriculture Organization of the United Nations (STATSGO-FAO) soil texture data set (based on wet techniques) using an advanced DPM in comparison to the LISA data set over Northern Africa and the Middle East. We explore the sensitivity of the drag partition scheme (a critical component of the DPM) and of the dust vertical fluxes (intensity and spatial patterns) to the roughness length and soil texture data sets. We also compare the use of the drag partition scheme to a widely used preferential source approach in global models. Idealized experiments with prescribed wind speeds show that the ERS and STATSGO-FAO data sets provide realistic spatial patterns of dust emission and friction velocity thresholds in the region. Finally, we evaluate a dust transport model for the period of March to July 2011 with observed aerosol optical depths from Aerosol Robotic Network sites. Results show that ERS and STATSGO-FAO provide realistic simulations in the region
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New insights into dust aerosol entrainment mechanisms from satellite/ground-based data, climate modeling, and wind-tunnel experiments
Atmospheric dust aerosols have implications for Earth’s radiation budget, biogeochemical cycles, hydrological cycles, human health, and visibility. Currently, there is a considerable mismatch between climate model simulations and observations in representing the dust cycle in terms of emission, transport, and deposition. This mismatch is related partly to our inadequate understanding of the complex dust emission processes and partly to the way these processes are represented in climate models. In this work, we examine these problems from various perspectives with an interdisciplinary approach by integrating wind-tunnel experiments, geomorphological mapping, satellite observations, land surface modeling, atmospheric reanalysis, and fully coupled earth system modeling.
The primary science contributions of this work are summarized here. First, we developed a detailed regional land cover map of the dust belt, the Middle East and North Africa. The developed map can be integrated in any regional dust models for better representing the spatial variation in dust source erodibility. We also developed a new observation-based soil erodibility map in global scale based on the correlation between reanalysis surface winds and satellite-observed aerosol optical depth data (AOD). Second, we integrated the developed observation-based erodibility map into the Community Earth System Model (CESM) and evaluated CESM’s performance in simulating mineral dust emission over the dust belt. Results show that the new erodibility map improves dust simulations in terms of AOD/dust optical depth (DOD) and the CESM captures large scale dust storms reasonably well when the winds are nudged towards ERA-Interim reanalysis data. Third, we conducted wind tunnel experiments and explored some of the lesser understood physical mechanisms of dust emission in sandblasting and direct aerodynamic entrainment. Results indicate that surface roughness can control dust emission in direct aerodynamic entrainment and that dust emission by direct aerodynamic entrainment can be significant under certain conditions compared to sandblasting. Lastly, we develop a principal component analysis based technique to extract locally mobilized dust component from the AOD data, which otherwise represent a mixture of several aerosol types and advected dust/aerosols.Geological Science
A Review of Current Methodologies for Regional Evapotranspiration Estimation from Remotely Sensed Data
An overview of the commonly applied evapotranspiration (ET) models using remotely sensed data is given to provide insight into the estimation of ET on a regional scale from satellite data. Generally, these models vary greatly in inputs, main assumptions and accuracy of results, etc. Besides the generally used remotely sensed multi-spectral data from visible to thermal infrared bands, most remotely sensed ET models, from simplified equations models to the more complex physically based two-source energy balance models, must rely to a certain degree on ground-based auxiliary measurements in order to derive the turbulent heat fluxes on a regional scale. We discuss the main inputs, assumptions, theories, advantages and drawbacks of each model. Moreover, approaches to the extrapolation of instantaneous ET to the daily values are also briefly presented. In the final part, both associated problems and future trends regarding these remotely sensed ET models were analyzed to objectively show the limitations and promising aspects of the estimation of regional ET based on remotely sensed data and ground-based measurements
Characterising Saharan Dust Sources and Export using Remote Sensing and Regional Modelling
The PhD-thesis aims to characterise the Saharan dust cycle at diffent seasons using satellite remote sensing techniques and regional modelling studies. A dust index based on 15-minute infrared satellite measurements provided by the SEVIRI instrument onboard the Meteosat Second Generation (MSG) satellite is used to infer spatio-temporal charcteristics of dust sources north of 5°N over Africa since March 2006. The spatial distribution of dust sources points towards the importance of endorehic drainage systems in mountain areas. The temporal distribution of the time-of-day when dust mobilisation starts shows maximum activity during local morning hours, pointing towards the role of the breakdown of the nocturnal low-level jet. Details of the role and ability of the low-level jet breakdown for dust entrainment were studied using regional modelling. Furthermore, the seasonal dust export towards the tropical North Atlantic is considered using regional modelling
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