Impact of Dust Long Range Transport on North American Monsoon

North American Monsoon has significant impact on the climate and the hydrological cycle at the northwestern Mexico and southwestern United States region. Recent studies from simulations generated by regional coupled atmosphere aerosol/chemistry model found that dust from deserts at Southwest United States has significant impact on North American Monsoon (NAM) circulation and precipitation. The direct radiative forcing from dust cools surface; warms near surface atmosphere and decreases the radiation at top of atmosphere. The dust induced diabetic heating increases the moisture flux convergence therefore enhances the precipitation in NAM region at monsoon season. In this study, the direct radiative forcing from dust and its impact on the NAM circulation and precipitation are investigated for the summer monsoon season at NAM region using NCEP operational global aerosol model NGAC. Besides dust emitted from deserts at Southwest United States, dust transported through the long range transport from West Africa Sahara region are also considered. The radiation forcing from these two dust sources are analyzed for the NAM monsoon season; the dust induced changes in atmosphere thermal structure, low level winds and the sea surface temperature are investigated; and the mechanism of how these changes influence the NAM circulation, precipitation and surface temperature are discussed.