The Aerosol-Monsoon Climate System of Asia

Abstract:

In this talk, I will discuss the variability of the coupled aerosol-monsoon climate system of South Asia and East Asia. It will be shown that possible interaction pathways include local effects through aerosol impacts on radiation, and microphysics of clouds, as well as non-local effects arising from aerosol emission, transport, and feedback processes involving changes in rainfall, moisture, winds, land-sea thermal contrast, heat sources and sink distributions in the atmosphere-ocean-land monsoon system. These interactions take place over a wide range of temporal scales from hourly to multi-decadal, and spatial scales from 1-10⁴km. Examples will be presented showing how elevated absorbing aerosols (dust and black carbon) may interact with monsoon dynamics to produce feedback effects on the atmospheric water cycle, leading to re-distribution of monsoon rainfall over South Asia, including possible accelerated melting of snowpack over the Himalayas and Tibetan Plateau. Based on CMIP5 model 20^th century simulations and future projections, we find that greenhouse gases generally increase Asian monsoon rainfall due to thermodynamic effects. However, solar dimming from increasing concentration of aerosols, could lead generally to a reduction of Asian monsoon rainfall. The net effect of climate change in monsoon is the residual of these two dominant forcing and responses. Regional monsoon changes predicted by CMIP5 models have large uncertainties, with high degree of variability among models, and are not comparable to observed rainfall trends. We suggest that large uncertainties in CMIP5 models are likely due to due to inadequate representation of regional aerosols processes.