The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

The South Asian summer monsoon (SASM) is of considerable scientific and social importance to the densely populated South Asia. Existing literature signified that the interannual variation of the SASM can be reflected by multiple dynamical and radiative processes. However, quantifying their relative contributions remains inadequate, particular for the contribution of aerosol process. Observational analysis indicates that the SASM circulations can be well depicted by the land-sea thermal contrast index (LSTCI), which is defined as temperature difference between the southern Eurasia (SE) and the tropical Indian Ocean (TIO) at the mid–upper troposphere. Based on the coupled atmosphere-surface climate feedback-response analysis method with the effects of aerosols incorporated (CFRAM-A), this study linearly decomposes the total temperature change associated with the LSTCI into several partial temperature changes associated with individual dynamical and radiative processes. Our result demonstrates that the LSTCI is mainly explained by the positive contributions of atmospheric dynamic (69%), water vapor (35%), and aerosol (11%) processes, which are partially offset by a negative contribution of cloud process (-18%). Surface dynamic process play a neglectable role in the LSTCI, because it exerts similar effects on the temperature anomalies over the SE and the TIO. Further analysis indicates that the total effect of aerosols is dominated by change in black carbon. As two important components, the temperature anomalies over the SE and the TIO separately account for about 55% and 45% to the LSTCI. Our finding provides a new insight onto quantitatively understanding the relevant processes involved in the SASM variation.
 

South Asian summer monsoon,quantitative attribution,interannual variation