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Scale‐invariance of albedo‐based wind friction velocity

Ziegler, Nancy P., Webb, Nicholas P., Chappell, Adrian and LeGrand, Sandra L. 2020. Scale‐invariance of albedo‐based wind friction velocity. Journal of Geophysical Research: Atmospheres 125 (16) , e2019JD031978. 10.1029/2019JD031978

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Abstract

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 MODIS 500 m) datasets. 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 (u s* ) is applicable across scales. The albedo‐based approach enables consistent and reliable drag partition correction across scales for model and field estimates of u s* necessary for wind erosion and dust emission modeling.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Publisher: American Geophysical Union (AGU)
ISSN: 2169-897X
Date of First Compliant Deposit: 3 August 2020
Date of Acceptance: 15 July 2020
Last Modified: 09 Sep 2020 12:30
URI: http://orca.cf.ac.uk/id/eprint/133914

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