Role of Atlantic SST in the Recent ENSO Predictability Change in NMME Model Hindcasts
Abstract The present study analyses the possible change in the seasonal prediction skill of El Nino Southern Oscillation (ENSO) in association with the reported climate modification in the tropical Pacific during the early 21st century. The hindcasts of nine models that participated in the National Multimodel Ensemble Project (NMME) are used for the analysis. Both the boreal summer (JJAS) and winter (DJF) seasons ENSO indices from 4 months and 1-month lead for the period 1981-2018/19 are studied. The analysis shows that all the models have reduced interannual variability as observations for both seasons. There is not much skill (both actual and potential) difference for DJF season for all the models for both the lead times. Summer skill loss for Feb IC is more for models such as CanSIPv2, CCSM3 and NEMO, while it is minimum for CCSM4. There is an increase of skill for Feb IC hindcasts for three GFDL models for JJAS season. Most of the models failed to simulate the ENSO events during the second period. The summer season ENSO pattern in the recent period are influenced by spring time north Atlantic SST anomalies. The models with maximum decrease of skill after 2000 fail to simulate the tropical Atlantic SST anomalies during the initialization months and also the summer season SST anomalies induced by these SST anomalies. The models with better or close to observed patterns with Atlantic SST induced ENSO patterns are only able to maintain the same skill as previous decades.