The primary goal of the proposal is to quantify the future projections of the Asian Summer Monsoon (ASM) and tropical Indian Ocean (TIO) climate systems. Specifically, the proposed research aims to examine:

1. The degree to which changes in greenhouse gas and aerosol (sulfate and black carbon) concentrations influence the time-mean state of the ASM and TIO
2. How do such changes influence the extended monsoon breaks (breaks that last for more than seven days), statistics associated with monsoon depressions, the frequency of severe droughts and floods (seasonal rainfall exceeding 20% of the normal), and persistence of drought/flood (continuous failure/success of the monsoon for more than 2 years)
3. The degree to which changes in the TIO climate impact regional and global climate variability including that of the Northern Hemisphere extratropical circulation for accurate projections of the North American climate.

The seasonal mean rainfall associated with the summer monsoon determines every pulse of the socio-economic sectors of Asia, the densely populated region in the world. Given their anticipated population rise, together with uncertainties in the future performance of the monsoon due to climate change, countries influenced by the ASM will surely face increased stress in the near future, which will seriously impact the stability of their social, economic, and political infrastructures. For example, in India, the successive failure of the summer monsoon rainfall in 1965 and 1966 together with the occurrence of below normal rainfall in 1968 and 1969 led to severe food scarcity, and in fact shortage of food was a nightmare during 1965-70. On the other hand, the strong Indian monsoon epoch of 1954-64 (persistence of above normal rainfall) was the stepping-stone for laying the foundation of India’s industrialization, spread of education, and setting-up of several scientific institutions across India. Therefore, reducing the uncertainties in model projections on the frequency of monsoon droughts at decadal to longer time scales require concentrated efforts. Since the ASM and TIO are intrinsically coupled at all time scales, projecting their future state with reduced uncertainties is the primary focus here. The proposal is built on a set of linked hypotheses:

1. The amount of solar radiation reaching the Earth’s surface depends on the radiative properties of two competing factors namely, anthropogenic greenhouse gases and absorbing-scattering aerosols
2. While both forcing elements affect the surface temperature distribution, aerosols influence the heating in the lower atmosphere, and snow cover albedo
3. The over-all effect is to induce changes in atmospheric circulation and rainfall that are amplified manifold by air-sea interaction processes over the TIO.

Since the two dominant forcing elements of climate change have opposite influences on the ASM projections, we propose that to reduce the uncertainties in the projections, coupled models that are employed in climate change experiments have realistic representation of the current basic state, and also capture the air-sea interaction processes over the TIO. The proposed hypothesis and related questions will be tested through analyses of observations/reanalysis products, IPCC AR4 integrations, and by obtaining a suite of sensitivity experiments with a range of models, both in idealized and realistic configurations. To achieve the target, we require high-end computing facilities, and the outcome is expected to make a “definitive statement” on the future projections of ASM, TIO and North American climate and their variations. The questions we propose to address are directly related to SciDAC call in the Climate Change Prediction Program, in particular to “Experiments using existing state-of-the-art climate model projections.” In addition, proposed work will also address systematic model errors and suggestions of improving them. The proposed effort lasts four years, and the requested budget is $758,126, including support for a graduate student and a post-doctoral fellow, thereby enhancing the workforce in climate change science that will be very much needed in the near future.