Relationships between the East Asian-western north pacific monsoon and ENSO simulated by FGOALS-s2

Abstract

The relationships between ENSO and the East Asian-western North Pacific monsoon simulated by the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 (FGOALS-s2), a state-of-the-art coupled general circulation model (CGCM), are evaluated. For El Nino developing summers, FGOALS-s2 reproduces the anomalous cyclone over the western North Pacific (WNP) and associated negative precipitation anomalies in situ. In the observation, the anomalous cyclone is transformed to an anomalous anticyclone over the WNP (WNPAC) during El Nino mature winters. The model reproduces the WNPAC and associated positive precipitation anomalies over southeastern China during winter. However, the model fails to simulate the asymmetry of the wintertime circulation anomalies over the WNP between El Nino and La Nina. The simulated anomalous cyclone over the WNP (WNPC) associated with La Nina is generally symmetric about the WNPAC associated with El Nino, rather than shifted westward as that in the observation. The discrepancy can partially explain why simulated La Nina events decay much faster than observed. In the observation, the WNPAC maintains throughout the El Nino decaying summer under the combined effects of local forcing of the WNP cold sea surface temperature anomaly (SSTA) and remote forcing from basin-wide warming in the tropical Indian Ocean. FGOALS-s2 captures the two mechanisms and reproduces the WNPAC throughout the summer. However, owing to biases in the mean state, the precipitation anomalies over East Asia, especially those of the Meiyu rain belt, are much weaker than that in the observation.