Aerosol-Cloud-Radiation Interaction Studies with GEOS-4 Model and Comparison with Observations

Abstract

Increasing human population and rapid urbanization in the last two decades have caused a sharp rise in anthropogenic aerosols particularly over South and East Asia. Numerous studies have shown that aerosols play an important role in climate change through their interaction with the global water and energy cycles. Thus Aerosol-cloud-radiation-monsoon interaction related droughts and floods are two of the most serious environmental hazards confronting more than 60% of the population of the world living in the Asian monsoon countries. General circulation models (GCMs) are an important tool for understanding the climate response to changes in the amounts and composition of aerosols due to evolving use of fossil and biomass fuels. This dissertation attempt to get an insight into the aerosol-cloud interaction and study impacts of aerosol forcing, with particular emphasis on the interaction of aerosol with monsoon water cycle. NASA Goddard Earth Observing System (GEOS) version 4 General Circulation Model (called GEOS4-GCM) with moist convection of Relaxed Arakawa–Schubert Scheme (McRAS) clouds and state-of-the-art parameterization of cloud microphysical process is used this study. A Single Column version (SCM) of the model is used to evaluate various parameterization schemes by comparing against in-situ and satellite observations. The model simulated realistic annual mean and annual cycles of cloud water, cloud optical thickness, cloud drop number concentration and effective radius without showing any systematic biases. GCM version of the model is used to study aerosol induced anomalies during summer months (June-August) particularly focusing over Indian monsoon. The individual aerosol effects (direct and indirect) and their combination show different impacts on radiation as well as on cloud microphysics, precipitation and circulation. However, complexities of nucleation of ice clouds in the model result not enough aerosols were acting as ice nuclei, which led to incomplete understanding of indirect effect in the atmosphere.