资源环境科技发展态势分析平台

The Indian summer monsoon (ISM) rainfall is often influenced by El Nino-Southern Oscillation (ENSO) on the interannual time scale. Physical mechanisms that link the canonical El Nino and ISM rainfall have been well documented. Very few studies have discussed the pathways that link El Nino Modoki and ISM rainfall variations. In this study using long period (1901-2014) reanalysis and observed rainfall data, it is found that rainfall anomalies are negative over the southern peninsular India and positive over the central parts of India during El Nino Modoki years. Detailed analysis suggests that the El Nino Modoki modulates ISM rainfall by inducing changes in the western north Pacific (WNP) low-level circulation. The weak positive rainfall over the monsoon trough region is due to weak moisture convergence associated with the westward extension of WNP cyclonic circulation corroborated by lows and depressions. Anomalous WNP cyclonic circulation is induced by the central Pacific Sea Surface Temperature (SST) warming associated with the El Nino Modoki. Further, strong moisture divergence over south peninsular India caused negative rainfall anomalies during the El Nino Modoki years. Thus, WNP circulation plays a critical role in determining the ISM rainfall patterns during the El Nino Modoki years as evidenced by significant correlation between WNP circulation pattern and EMI. These regional rainfall patterns over the Indian subcontinent corresponding to El Nino Modoki are not well explained in previous studies. It is found that many Coupled Model Intercomparison Project Phase 5 (CMIP5) models displayed poor skill in representing the relation between ISM rainfall and El Nino Modoki events due to unrealistic simulation of SST and circulation patterns over the Indo-Pacific region. This suggests that CMIP5 models tend to have a large diversity in representing the El Nino Modoki teleconnections to ISM rainfall.