Other
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p13b0157y&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #P13B-0157
Other
0305 Aerosols And Particles (0345, 4801, 4906), 0312 Air/Sea Constituent Fluxes (3339, 4504)
Scientific paper
The role of direct radiative forcing of dust in causing the Sahelian drought observed in the last three decades of 20th century is investigated using simulations with an atmospheric general circulation model. Our model produces smaller shortwave and larger longwave forcings of dust than other simulation studies mainly due to the difference in particle size.produces smaller shortwave and larger longwave forcings of dust than other simulation studies mainly due to the difference in particle size distributions. Simulations produce reduced rainfall over the intertropical convergence zone (ITCZ) including the Sahel region and increased rainfall south of ITCZ when dust radiative forcing is included. These occur due to the cooling of global tropical oceans as well as the cooling of the troposphere over North Africa in response to dust radiative forcing. Simulations forced by observed sea surface temperatures (SSTs) with or without dust radiative forcing produce decrease of Sahel rainfall and increase of North African dust from 1950s to 1980s, but underestimate the magnitudes of observed changes. It is found that effects of simulated changes in Atlantic and Indian Ocean SSTs, dust, vegetation, and greenhouse gas warming can explain about 70 percent of the precipitation changes in Sahel between wet and dry periods. Dust accounts for about 20 percent of the observed change in our model simulations and two thirds of this comes through cooling the troposphere over North Africa. The dust impact on Atlantic SST is of a secondary importance. Both greenhouse gas warming of the Indian Ocean and vegetation loss in Sahel account for about 25% of the observed trend in our simulations. Processes excluded in the simulations such as land use impacts on dust, dynamic vegetation feedbacks, and indirect radiative effects, or errors in the model could be responsible for the remaining differences between observed and simulated precipitation changes
Collins William
Conley Alex
Fillmore David
Mahowald Natalie
Yoshioka Masahiko
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