The influence of Tropical Indian Ocean SST on the Indian summer monsoon

The Indian Summer Monsoon (ISM) is the main component of the Asian summer monsoon. It is well known that one of the starting mechanism of a summer monsoon is the thermal contrast between land and ocean and that SST and moisture are crucial factors for its evolution and intensity. The Indian Ocean may play a very important role in the beginning and evolution of the ISM itself. A coupled general circulation model, implemented with a high resolution atmospheric component, appears to be able to simulate the Indian summer monsoon in a realistic way. In particular, the features of the simulated ISM variability are similar to the observations.The model is used to study the effects of the Tropical Indian Ocean SST anomalies on monsoon precipitation over India. A statistical method, the "coupled manifold", is used to investigate the Tropical Indian Ocean SST variability and its relation with the Tropical Pacific Ocean. The analysis shows that the SST variability in the TIO contains a significant portion that is dependent from the TPO variability. The same technique is used to estimate the amount of Indian rainfall variability that can be explained by the Tropical Indian Ocean SST. Overall, the Indian monsoon precipitation is largely influenced by the TIO SSTA and when the Indian Ocean SSTA are separated in a part remotely forced from the Tropical Pacific Ocean variability and a part independent from that, the forced part has a larger impact.