Different Impacts of Typical and Atypical ENSO on the Indian Summer Rainfall: ENSO-Developing Phase

The El Nino-Southern Oscillation (ENSO) is a main driving force of the northern hemisphere summer monsoon rainfall, including the Indian Summer Rainfall (ISR). The impacts of typical ENSO and atypical ENSO events on the ISR remain unclear during their developing summers. This study examines the different linkages between a typical ENSO and the ISR and between an a typical ENSO and the ISR. During the developing summer of a typical El Nino, negative rainfall anomalies are seen over the northeastern Indian subcontinent, while the anomalous rainfall pattern is almost the opposite for a typical La Nina; as for an atypical ENSO, the approximate linear opposite phenomenon vanishes. Furthermore, an anomalous global zonal wave train is found at mid-latitudes, with a local tripole circulation pattern over central-eastern Eurasia during the developing summer of a typical ENSO, which might explain the corresponding rainfall response over the Indian Peninsula. By contrast, such features are not obvious during the developing summer of an atypical ENSO. Among 106-year historical runs (1900-2005) of nine state-of-the-art models from the Coupled Model Intercomparison Project, Phase 5 (CMIP5), HadGEM2-ES exhibits promising skill in simulating the anomalous circulation pattern over mid-latitudes and central-eastern Eurasia. Probably, it is the model's ability to capture the linkage between a typical ENSO and the ISR and the characteristics of a typical ENSO that makes the difference.