The Indian Ocean-origin seasonal rainfall predictability in the South and Southeastern Asian summer monsoons

Seasonal prediction of the Asian summer monsoon has long been considered to be notoriously difficult due to the complexity of the atmosphere-ocean-land interaction. Latest climate prediction models present some meaningful prediction skill in predicting the interannual variability in some parts of South and Southeast Asia, however, underlying mechanisms giving rise to the prediction skill are not still fully understood. Recently, it was proposed that the Indian Ocean warming by a delayed effect of the El Niño-Southern Oscillation (Indo-western Pacific Ocean Capacitor mode; IPOC mode) has a significant influence on the regional South Asian interannual rainfall variability in summer following El Niño. In this study, a large ensemble hindcast experiment of 52-members during 37 years (1980- 2016) starting from the end of April using Japan Meteorological Agency seasonal prediction system (JMA/MRI-CPS2) was performed and analyzed. Results in this study present meaningful skill (correlation coefficient > 0.4) in predicting seasonal rainfall in some regions such as the Ganges basin, the Arabian Sea and Indonesia. A singular value decomposition analysis of sea surface temperature and rainfall amount suggest that the rainfall variability and prediction skill are associated with IPOC mode. Moreover, results of a sensitivity hindcast experiment, in which sea surface temperature in the Indian Ocean was relaxed to a climatology, indicate a large impact (more than 50 % of the total interannual variance) of the Indian Ocean on summer rainfall amounts from the Arabian Sea to the Bay of Bengal. The results obtained in this study confirm that the Indian Ocean plays a dominant role in modulating the interannual rainfall variability in the surrounding Asian regions. The better representation of the precipitation variability pattern associated with the IPOC mode is a key to produce skillful rainfall predictions in South and Southeast Asia.