WRF-Chem simulations of a typical pre-monsoon dust storm in northern India: Influences on aerosol optical properties and radiation budget

The impact of a typical pre-monsoon season (April-June) dust storm event on the regional aerosol optical properties and radiation budget in northern India is analyzed. The dust storm event lasted from 17 to 22 April 2010 and the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) estimated total dust emissions of 7.5 Tg over the model domain. Both in situ (AERONET -Aerosol Robotic Network) and satellite observations show significant increase (> 50 %) in local to regional scale aerosol optical depth (AOD) and decrease (> 70 %) in the Angstrom exponent (alpha) during this period. Amongst the AERONET sites in this region, Kanpur was influenced the most, where the AOD reached up to 2.1 and the alpha decreased to -0.09 during the dust storm period. The WRFChem model reproduced the spatial and temporal distributions of dust plumes and aerosol optical properties but generally underestimated the AOD. The average MODIS and WRF-Chem AOD (550 nm) values in a subregion (70-80 degrees E, 25-30 degrees N) affected the most by the dust storm are estimated as 0.80 +/- 0.30 and 0.68 +/- 0.28, respectively. Model results show that dust particles cool the surface and the top of the atmosphere, but warm the atmosphere itself. The radiative perturbation due to dust aerosols averaged over the subregion is estimated as -2.9 +/- 3.1 W m(-2) at the top of the atmosphere, 5.1 +/- 3.3W m(-2) in the atmosphere and -8.0 +/- 3.3 W m(-2) at the surface. The simulated instantaneous cooling under the dust plume was much higher and reached -227 and -70 W m(-2) at the surface and the top of the atmosphere, respectively. The impact of these radiative perturbations on the surface energy budget is estimated to be small on a regional scale but significant locally.