On the Impacts of the Indian Summer Monsoon on ENSO in A Coupled GCM
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This study explores the impacts of the Indian summer monsoon (ISM) on the El Niño-Southern Oscillation (ENSO) evolution by utilizing two coupled general circulation model simulations. The first simulation uses the Center for Ocean-Land-Atmosphere Studies (COLA) anomaly coupled model and the second simulation employs a new coupling strategy, interactive ensembles, that is designed to increase the signal to noise ratio. The effects of monsoon variability related and unrelated to ENSO are separated through composites in terms of both Niño-3.4 sea surface temperature (SST) and Indian summer monsoon rainfall (IMR) anomalies. It is found that ENSO-related monsoon variability has significant impacts on warm events. In the interactive ensemble simulation, a weak (strong) monsoon enhances (weakens) an ongoing warm event. The monsoon impacts are manifested in the surface zonal wind stress anomalies in the western-central equatorial Pacific. In the anomaly coupled simulation, the monsoon- ENSO relationship is difficult to detect. The ongoing cold events are only weakly affected by monsoon variability. Monsoon variability that is unrelated to ENSO also induces noticeable SST anomalies in the equatorial central Pacific in the following winter. In the interactive ensemble model, a weak (strong) monsoon induces noticeable warm (cold) SST anomalies.
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