The Influence of Aerosol Hygroscopicity on Clouds and Precipitation over Western Ghats, India

We examine the role of aerosol hygroscopicity (κ) affects clouds and precipitation formation over the Western Ghats (WG) in India using various numerical model simulations (i.e., particle-by-particle based small-scale, high resolution mesoscale model). For the diffusional growth of cloud droplets, the size dependent hygroscopicity is used in κ- Köhler equation of direct numerical simulation. The results of the small-scale model reveal that the distribution of cloud drop size varies from the initial mixing state to well mix state due to variation in κ. The value of κ is obtained from HTDMA instruments at High Altitude Cloud Physics Laboratory, India. The idealized and real simulations using WRF model with aerosol-aware Thompson microphysics scheme are conducted by changing κ values. Depending on the type of clouds (shallow or deep), different κ values determine the mass, number and precipitation of cloud and rain droplets. Low hygroscopicity (organics) simulates more and smaller drops, as well as uplifts below freezing level, resulting in more ice phase hydrometeors. Organic aerosols have a significant impact on the formation of more snow and graupel hydrometeors. As compared to high κ, low hygroscopicity weakens updrafts at the intermediate level and strengthens them at the upper level in the deep cloud region. The intensity of precipitation varies due to low and high κ. The findings indicate that aerosol composition has a significant impact on the activation of cloud condensation nuclei. This study suggests that aerosol hygroscopicity is essential in weather prediction models in order to integrate aerosol chemical compositions.