Seasonal Prediction of Distinct Climate Anomalies in Summer 2010 over the Tropical Indian Ocean and South Asia

The characteristics and predictability of climate anomalies over the tropical Indian Ocean (TIO) and South Asian region during the boreal summer (June-July-August) of 2010 are investigated on the basis of atmospheric regional model simulations and five forecasts obtained from Asia-Pacific Economic Cooperation Climate Center coupled models. The robust features of summer 2010 are the basin-wide TIO warming and enhanced (suppressed) rainfall over the north Indian Ocean and maritime continent (head Bay of Bengal and parts of monsoon trough region). Our regional atmospheric model experiments corroborate that rainfall over South Asia was mostly determined by the TIO sea surface temperature (SST) warming during summer 2010. Most of the coupled models and their multi-model ensemble (MME) used in this study successfully predict the robust features over the TIO and/or South Asian region with 01 May 2010 initial condition. The positive rainfall anomalies over the west coast of India, southern Peninsular India, and central Bay of Bengal are qualitatively well predicted by the MME. Suppressed rainfall over the northeast Bay of Bengal associated with the northwestward extension of the northwest Pacific ridge is also reasonably predicted by the MME. On the other hand, the MME has a moderate skill in predicting positive rainfall anomalies over the convective zone of southeast TIO due to weak local SST warming. Further, the coupled models and their MME fail to predict the anomalous positive rainfall in northern Pakistan because of their inability in predicting mid-latitude circulation anomalies. This study reveals that the predictive skill of rainfall and circulation anomalies during summer 2010 over the TIO and South Asia is largely attributable to the Indian Ocean basin-wide warming during the decay phase of El Niño. These results indicate that the accurate simulation of the TIO SST by coupled models is critical in determining the 2010 South Asian summer monsoon rainfall.