Aerosols impact on the convective and non-convective rain distribution over the Indian region: Results from WRF-Chem simulation

Abstract

The Weather Research and Forecasting (WRF) model coupled with chemistry (WRF-Chem) is used to simulate rainfall pattern over the Indian landmass during a normal monsoon year (June–September 2010). Sensitivity analysis is performed using three different microphysical (MP) schemes (Thompson, Morrison, and Lin) to simulate the rainfall pattern and distribution over India. A significant difference in the rainfall amount, as well as distribution, is observed among the MP schemes, despite using the same model configuration and the meteorological and chemical initial and boundary condition. Lin MP scheme performed better than other schemes in simulating the rainfall over the Indian domain. Heavy rainfall along the foothills of the Himalayas, the mountainous coastal region of western India, and the northeastern part of India and sparse rainfall over northwest India are captured realistically in the model, which agrees well with the observed rainfall pattern over India. The spatial distribution of aerosol optical depths retrieved from the MODIS satellites is broadly well simulated by the model.The model simulated convective and non-convective rainfall characteristics over the Indian landmass are found to be consistent with the monsoon precipitation climatology. It is shown that the change in both convective and non-convective rainfall due to aerosols and chemistry is non-negligible over India during monsoon season. The total rainfall is found to increase significantly over the entire Western Ghats and some part of northeast India, while it is diminished over the northwest, north and east India when aerosol chemistry effects are considered in the model simulation. Additional analysis is performed to simulate the perturbations in convective and non-convective rainfall due to aerosols (e.g., dust, sea salt, black carbon etc.). Results show that the effect of aerosols on convective and non-convective rainfall distribution over India is non-linear. Depending on the meteorological conditions, topography, and the type of aerosol, the aerosol impact and feedback on monsoon rainfall can be positive, negative, or neutral.