Effects of mineral aerosols on the summertime climate of southwest Asia: Incorporating subgrid variability in a dust emission scheme

Title Effects of mineral aerosols on the summertime climate of southwest Asia: Incorporating subgrid variability in a dust emission scheme
Publication Type Journal Article
Year of Publication 2010
Authors Marcella MP, Eltahir EAB
Journal Journal of Geophysical Research
Volume 115
Pagination D18203
Improvements in modeling mineral aerosols over southwest Asia are made to the dust
scheme in a regional climate model by representing subgrid variability of both wind
speed and surface roughness length. The new module quantifies wind variability by using
model meteorology while assuming that wind speed follows a Gaussian distribution. More
specifically, wind variability is approximated by dry convective eddies within the
planetary boundary layer, forced by sensible heat fluxes at the surface. Incorporating
subgrid variability of wind increases aerosol optical depth (AOD) over the region by
nearly 35% while reducing incoming shortwave radiation by an additional 5–10 W/m2.
Likewise, the dust scheme is modified to include the variability of surface roughness
length over southwest Asia. Here an empirical distribution of roughness length for each
grid cell is calculated based on the USGS’s 4 km resolution land cover data set. However,
incorporating roughness length variability does not significantly alter dust emissions over
the region due to the relatively homogeneous land cover conditions. Nevertheless,
including spatial variability for wind results in aerosol optical depth values closer to
observational data sets, particularly MISR, which performs better than MODIS over this
region. However, RegCM3’s dust model still underestimates AOD over southwest Asia.
In addition to improvements made in RegCM3’s dust model, this work examines the
effects of mineral aerosols on the mean monthly, surface summertime climate of southwest
Asia. It is shown that dust emissions reduce average summertime surface temperatures
by approximately 0.5°C while attenuating shortwave incident radiation by nearly
25 W/m2. Thus, the emission of dust is an important surface process in shaping the
summertime climate over southwest Asia. However, both a warm bias in surface
temperatures and overestimation of incoming shortwave radiation still exist in RegCM3
and need to be further addressed.
Relevant Projects:
Regional Climate Modeling over Semi-Arid Regions
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