Influences of spring-to-summer sea surface temperatures over different Indian Ocean domains on the Asian summer monsoon

The influences of spring-to-summer sea surface temperature (SST) anomalies in different domains of the Indian Ocean (IO) on the Asian summer monsoon are investigated by conducting a series of numerical experiments using the NCAR CAM4 model. It is found that, to a certain extent, the springtime IO SST anomalies can persist to the summer season. The spring-to-summer IO SST anomalies associated with the IO basin warming mode are strongly linked to the summer climate over Asia, especially the South Asian monsoon (SAM) and the East Asian monsoon. Among this connection, the warming of tropical IO plays the most critical role, and the warming of southern IO is important for monsoon variation and prediction prior to the full development of the monsoon. The atmospheric response to IO basin wide warming is similar with that to tropical IO warming. The influence of northern IO warming on the SAM, however, is opposite to the effect of southern IO warming. Meanwhile, the discrepancies between the results from idealized SST forcing simulations and observations, especially for the southern IO, reveal that the dominant role of air-sea interaction in the monsoon-IO coupled system cannot be ignored. Moreover, the springtime northern IO warming seems to favor an early onset or a stronger persistence of the SAM.