Citation:

GILLETTE, D. EXPRESSING SUPPLY LIMITATION IN SAND SALTATION. Presented at First Sino-USA Conference on Environments and Mechanics, Lanzhov, CHINA, September 28 - 29, 2006.

Impact/Purpose:

The objectives of this task include: (1) to continuously evaluate and analyze the forecast results to provide diagnostic information on model performance and inadequacies to guide further evolution and refinements to the CMAQ model, and (2) extending the utility of the daily air quality forecast model data being produced by NOAA's National Weather Service (NWS) as part of a NOAA/EPA collaboration in air quality forecasting, to EPA mission-oriented activities. These objectives include developing and maintaining a long-term database of air quality modeling results (ozone and PM2.5), performing periodic analysis and assessments using the data, and making the air quality database available and accessible to States, Regions, RPO's and others to use as input data for regional/local scale air quality modeling for policy/regulatory purposes.

Description:

Saltation-driven sandblasting is the most effective producer of windblown dust. Modeling of wind-blown dust emissions requires an efficient parameterization of sand flux in the saltating mode. According to the theory of P. R. Owen the horizontal mass flux of saltating uniform particles is equal to a coefficient AO times a function using three parameters: friction velocity, threshold friction velocity, and the ratio of air density to the acceleration of gravity. We compared Owen's expression for AO with the ratio of the measured horizontal flux of saltating particles to Owen's expression for saltating sand when AO was set to 1. We called this ratio "A." AO was part of Owen's model whereas "A" is a value that forces Owens model to agree with our measured sand flux. Values of A in can be used to (1) characterize the efficiency of the wind to move sand by saltation for different soil textures and aggregations, and (2) to make practical predictions of sand movement based on the condition of the surface soil and (3) to delimit a surface that is "supply limited," that is, normal saltation is not possible because sand particles available for entrainment are limited.

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