[A-CG47] 海洋と大気の波動・渦・循環の力学

[ACG47-P04] Numerical study on the covariability of ENSO and Indian Ocean SST influence

*Zhuoqi HE¹、weiqiang wang¹ (1.South China Sea Institute of Oceanology, Chinese Academy of Sciences)

キーワード：CESM, ENSO, Indian Ocean SST, climate effect

We adopt both observational analysis and numerical experiment to demonstrate that the winter western Indian Ocean (WIO) sea surface temperature anomalies (SSTA) can influence on the western Pacific climate either independently or under governed by El Niño – South Oscillation (ENSO). These two cases exhibit distinct physical processes. In ENSO years, the winter WIO SSTA displays a negative relationship with the western Pacific rainfall with double extremums in winter and summer. In winter, the concurrence of positive SSTA in the WIO and the eastern Pacific directly suppresses convection in the western Pacific via an anomalous reversed large-scale Walker circulation. In the following summer, the North Indian Ocean and the Southeast Indian Ocean warming develops via series of air-sea interaction processes. The ocean warming in these two regions jointly drives an anomalous vertical circulation and results in the second decrease of rainfall over the western Pacific. In non-ENSO years, the winter WIO SSTA shows an out-of-sign relationship with the western Pacific rainfall anomaly with only one extremum in summer. In winter, the WIO warming alone induces equatorial westerlies in the western Indian Ocean and the western Pacific rainfall anomaly is insignificant during winter. In the following summer, the wind-driven coastal downwelling effect and the Kelvin wave propagation lead to a deep warming over the Southeast Indian Ocean. This deep ocean warming invigorates an anomalous atmospheric meridional circulation, which in turn suppresses the summer western Pacific rainfall. The Community Earth System Model (CESM) pacemaker experiments are further employed to confirm these different air-sea responses in the above ENSO and non-ENSO cases.