Effect of multi-decadal variation of SST on rainfall and dust transport over West Africa and northern Atlantic Ocean

Effects of multi-decadal variation of SST on the West African monsoon rainfall and circulation, and consequent change in dust emission and transport are examined based on model experiments with NASA GEOS-5 GCM with prescribed SST. Based on Singular Value Decomposition (SVD) between Sahel rainfall and global SST distribution, SST patterns representing 1950's and 1980's are selected and prescribed for 7-year simulation for each experiment. With 1950's SST, model produced weakened subtropical high, stronger cross equatorial flows, and enhanced rainfall in ITCZ and Sahel compared to the 1980's. Due to weakened surface winds, dust emission is reduced over the most of Sahel. Dust transport is reduced in the deep tropics, due to an increased wet deposition in the ITCZ and a weakening of the subtropical high. Increased dust transport associated with more frequent Saharan dust outbreak is found between 20N-25N. To examine the effect of aerosol radiative forcing, additional experiments are conducted by disabling dust radiative feedback. In this talk, the role of increased dust radiative forcing during dry Sahel on the West Africa monsoon rainfall and circulation will be also discussed.