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

Abstract

The impact of a typical pre-monsoon season (April–June) dust storm event on the regional aerosol opti- cal properties and radiation budget in northern India is an- alyzed. 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 obser- vations show significant increase (> 50 %) in local to regional scale aerosol optical depth (AOD) and decrease (> 70 %) in the Ångström exponent (α) 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 α de- creased to −0.09 during the dust storm period. The WRF- Chem model reproduced the spatial and temporal distribu- tions of dust plumes and aerosol optical properties but gen- erally underestimated the AOD. The average MODIS and WRF-Chem AOD (550 nm) values in a subregion (70–80◦ E, 25–30◦ 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 at- mosphere, but warm the atmosphere itself. The radiative per- turbation 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 ± 3.3 W 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, re- spectively. The impact of these radiative perturbations on the surface energy budget is estimated to be small on a regional scale but significant locally.