Diversifying impacts of El Niño/La Niña 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 Niño–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 Niño events show above-normal rainfall and remaining show below-normal rainfall over the SPI region, indicating the diversifying effect of El Niño on NEM rainfall. In the case of pure La Niña events, below-normal NEM rainfall is seen in 86% of events and above-normal rainfall in the remaining 14% of events. All El Niño–positive IOD (La Niña–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 Niño and La Niña 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 Niño events. This would certainly limit the CMIP5 models’ ability to accurately represent ENSO teleconnections to NEM rainfall over the SPI region.

在观测和耦合模型比对项目第五阶段（CMIP5）模型中，探索了厄尔尼诺/拉尼娜事件对印度东北半岛（SPI）东北季风（NEM； 10月至12月）降雨的多种影响。对观测结果的分析表明，在NEM季节（10月至12月），大约30％至40％的厄尔尼诺-南方涛动（ENSO）事件与印度洋偶极子（IOD）同时发生。从观察结果中可以发现，在SPI地区，大约有一半的纯厄尔尼诺事件显示出高于正常水平的降雨，其余部分则显示出低于正常水平的降雨，这表明厄尔尼诺现象对NEM降雨的影响是多样化的。就纯拉尼娜事件而言，在86％的事件中观测到NEM降雨低于正常水平，而在其余14％的事件中观测到高于正常降雨水平。在厄尔尼诺（ElNiño）阳性IOD（拉尼娜阴性IOD）同时发生的年份，SPI地区降雨正异常。与正/负湿度异常有关的南海气旋/反气旋环流的强度和位置主要是ENSO事件期间SPI上降雨模式差异的原因。发现在CMIP5模型中，SPI降雨模式的多样性不仅限于纯ElNiño和LaNiña案例，而且在ENSO-IOD共同关注的年份中也很突出。与纯粹的厄尔尼诺事件期间的观测结果相比，CMIP5模型显示出SPI地区向负降雨的强烈偏斜。这肯定会限制CMIP5模型准确表示ENSO与SPI地区NEM降雨的遥相关的能力。