A study of climate model responses of the western Pacific subtropical high to El Niño diversity

This study examines a climate model hindcast of the responses of the western Pacific subtropical high (WPSH) to three types of El Nino events: the Eastern Pacific (EP) El Nino and the types I and II of Central Pacific (CP-I and CP-II) El Nino. These El Nino types differ from each other in the central locations and patterns of their sea surface temperature (SST) anomalies. They invoke four different mechanisms to impact the WPSH. Hindcasts produced by the Taiwan Central Weather Bureau (CWB) Climate Forecast System 1-tiered model (TCWB1T1) are analyzed. These hindcasts realistically simulate the impacts on the WPSH during the CP-I El Nino, but overestimate the impacts during the decaying summer of the EP El Nino and during the developing autumn and early winter of the CP-II El Nino. The overestimates are mainly the result of an overly strong Maritime Continent regional circulation mechanism during EP El Ninos and an overly strong Indian Ocean capacitor mechanism during CP-II El Ninos. Further analyses show that these model biases are related to biases in the simulations of El Nino SST anomalies and the Walker circulation. Both model deficiencies are common to contemporary coupled climate models.