Asymmetric responses of the Philippine Sea anomalous anticyclone/cyclone to two types of El Niño–Southern Oscillation during the boreal winter

Abstract

The Philippine Sea anomalous anticyclone/cyclone (abbreviated to PSAC/PSCC) induced by El Niño/La Niña is a key atmospheric circulation system that connects El Niño/La Niña to the East Asian climate. The asymmetry between PSAC and PSCC is analyzed after El Niño–Southern Oscillation (ENSO) is divided into eastern Pacific (EP) ENSO and central Pacific (CP) ENSO. For EP ENSO, evident asymmetry exists between EP El Niño‐induced PSAC and EP La Niña‐induced PSCC, with the former being much stronger than the latter, caused by the nonlinearity of the convective anomalies over the western Pacific. Much stronger sea surface temperature (SST) anomalies for EP El Niño than for EP La Niña is responsible for this convective heating asymmetry.However, the PSAC and PSCC associated with CP ENSO show much weaker asymmetry compared with those associated with EP ENSO, which is related to the nearly symmetric distribution and intensity of the tropical SST anomalies between CP El Niño and CP La Niña. The resultant almost symmetric anomalous Walker circulation and the comparable convective anomalies over the western Pacific produce weak asymmetric responses of PSAC and PSCC to CP El Niño and CP La Niña. Furthermore, numerical experiments also confirm that the asymmetry in the anomalous convective activity over the western Pacific associated with EP (CP) ENSO is the main reason for the asymmetry between PSAC and PSCC.