Diversity in ENSO remote connection to northeast monsoon rainfall in observations and CMIP5 models

Diversifying impacts of El Nino/La Nina events on northeast monsoon (NEM; October to December) rainfall over southern peninsular India (SPI) are explored in observations and Coupled Model Inter-comparison Project Phase 5 (CMIP5) models. Analysis of observations suggests that about 30 to 40% of El Nino–Southern Oscillation (ENSO) events co-occurred with Indian Ocean Dipole (IOD) during the NEM season (October to December). It is found from the observations that approximately half of the pure El Nino events show above-normal rainfall and remaining show below-normal rainfall over the SPI region, indicating the diversifying effect of El Nino on NEM rainfall. In the case of pure La Nina events, below-normal NEM rainfall is seen in 86% of events and above-normal rainfall in the remaining 14% of events. All El Nino–positive IOD (La Nina–negative IOD) co-occurrence years have witnessed positive rainfall anomalies over the SPI region. The strength and position of cyclonic/anticyclonic circulation over the South China Sea associated with positive/negative moisture anomalies are mainly responsible for the differences in rainfall patterns over SPI during ENSO events. It is found that in CMIP5 models the diversity in SPI rainfall pattern is not just limited to only pure El Nino and La Nina cases but also prominent in ENSO-IOD co-concerning years. CMIP5 models displayed strong skewness towards negative rainfall over the SPI region as compared with the observations during pure El Nino events. This would certainly limit the CMIP5 models’ ability to accurately represent ENSO teleconnections to NEM rainfall over the SPI region.