Absorbing Aerosols and Aerosol Cloud Interactions Using Satellite Observation and Numerical Simulations

Abstract

Absorbing aerosols are among the most significant climatic agents whose role in modulating Earth s climate is still poorly understood. They absorb light, thereby reducing the surface-reaching solar radiation and heat their surroundings, resulting in modulation of atmospheric temperature and moisture profile. Thus these particles affect the micro and macrophysical properties of the cloud without participating in droplet formation. However, as particles spend more time in the atmosphere and interact with the other particles and gases, they may attain higher hygroscopicity. In consequence, they possess a range of hygroscopicity and also directly modulate the ambient environment. Hence contrary to scattering counterpart, absorbing aerosols show more complex interactions with clouds, thereby exacerbating the uncertainty in estimating radiative forcing associated with aerosol-cloud interactions (ACI). This dissertation investigates some aspects of absorbing (with a specific focus on mineral dust) aerosols and warm-cloud interactions using satellite observations, reanalysis data, and state-of-the-art numerical models. newlineThe signature of anthropogenic activity on cloud parameters was quantified using long-term ground-based and space-borne observations. Analysis over the Indo-Gangetic Plain, one of the world s most polluted and densely populated regions, reveals that anthropogenic aerosols, in terms of enhanced loading on working days (Monday to Friday), may reach up to +20 % as compared to the weekly mean. This enhanced aerosol loading results in 10 % additional atmospheric warming over a large area. It is found that high aerosol loading periods are the ones with optically thinner (lower cloud optical depth) and wider (increased cloud fraction) clouds with lower cloud heights (increased cloud top temperature and pressure). Using Clouds and the Earth s Radiant Energy System (CERES) derived radiative fluxes, a reduction in top of atmospheric shortwave (and#8722;5 %) and longwave cloud radiative effects (CRE) (and#8722;10 %) was observed.