The Impact of Anomalous Aerosol Heating on the Onset of the Asian Summer Monsoon

The study presented examines the impact of anomalous aerosol heating on the transition and early active phases of the south Asian monsoon. Aerosol direct and indirect effects represent radiative forcings which can modify tropospheric temperature profiles and extend cloud lifetimes. Recent studies have suggested that over monthly to seasonal time scales, these effects can lead to modified flow and rainfall regimes in the Asian monsoon region. Of special interest is the covariance of heating and temperature prior to active monsoon onset. It can be shown that anomalous generation of available potential energy due to aerosol radiative effects has the potential to impact the cascade of energy from the Hadley circulation to the monsoon eddy. In order to quantify the potential impact and the resulting changes in monsoon onset timing and rainfall, the WRF/CHEM regional weather and chemistry model is used to create an ensemble of forecasts for the south Asian monsoon region during May June and July. The forecasts with aerosol direct and indirect effects are compared to a control forecast without aerosols. The evolution of Irrotational and non-divergent kinetic energy, generation of available potential energy, baroclinic/barotropic instability and rainfall are presented.