Reexamining the Indian Summer Monsoon Rainfall-ENSO Relationship From Its Recovery in the 21st Century: Role of the Indian Ocean SST Anomaly Associated With Types of ENSO Evolution

This study found that the relationship between the Indian Summer Monsoon Rainfall (ISMR) and El Nino-Southern Oscillation (ENSO) has recovered since 2001, and the relationship strength is closely related to the summer tropical Indian Ocean (TIO) sea surface temperature (SST) anomaly, with the TIO warming (cooling) indicating a stronger (weaker) relationship. Under the same El Nino/La Nina scenario, different signs of the TIO anomaly indicate distinct atmospheric circulation anomalies over the Indian Ocean, thus affecting the ISMR-ENSO relationship. The TIO anomaly is principally associated with different types of ENSO temporal evolution. Strong El Nino events with an early onset, and the transition of El Nino to La Nina, tend to have a warmer TIO and a stronger ISMR-ENSO relationship, in contrast to most of the cases of a decaying La Nina or a La Nina that persists throughout the year. The result brings a prospect for improving the ISMR prediction.