A novel index for depicting ENSO transition with application in ENSO-East Asian summer monsoon relationship

Abstract

The impact of El Niño-Southern Oscillation (ENSO) transition on the East Asian summer monsoon (EASM) during post-ENSO summer has been investigated widely, but how to quantify ENSO transition precisely is still a challenge. This study proposes a new index to quantify ENSO transition based on the intensity of the spring persistence barrier. After validation through the key processes that influence ENSO transition, the index could be further validated by investigating the relationship between transitive/persistent ENSO events and the EASM. For the transitive ENSO events, the cold sea surface temperature (SST) anomaly in the central Pacific during post-ENSO summer strengthens the anticyclone over the western Pacific and the EASM by reinforcing the Walker circulation and the local Hadley circulation. In contrast, during the persistent ENSO events, the prolonged warm SST anomaly in the central Pacific exerts a relatively weaker impact on the EASM due to a less robust atmospheric response over the western Pacific.