Physics
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....13702c&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #13702
Physics
Scientific paper
The representation of dust emission in the NASA GISS AGCM is handicapped by the model's low resolution (4x5) compared to the scale of circulations that emit dust (including dust devils and haboobs). The current AGCM emission is tuned by altering the threshold velocity to match emission calculated by relatively high resolution offline tracer models. This approach has the disadvantage of being limited to the current climate, where high resolution reanalyses of surface wind speed are available to drive an offline model. We reintroduce a geographically uniform threshold, and use AGCM physics to identify regions where small scale circulations raise dust. We assume a distribution of wind speed within each grid box, and parameterize the standard deviation using wind velocity scales derived from the AGCM's parameterizations of the planetary boundary layer, along with dry and moist convection. This distribution allows dust to be raised even if the resolved wind speed is below the threshold, so long as there is ample subgrid variability. We find that dry convective thermals have the largest effect upon emission. This allows emission to increase over the Sahara and Taklimakan deserts, two regions where emission is underestimated when the threshold is tuned. This brings the model into better agreement with TOMS and AERONET observations of dust optical thickness, although there is excessive summertime emission over Australia and the southwestern US.
Cakmur R.
Miller Robert R.
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