Linear respective roles of El Niño–Southern Oscillation and East Asian winter monsoon in the formation of the western North Pacific anticyclone

Abstract

Based on reanalysis data, we investigate the respective roles of the East Asian winter monsoon (EAWM) and El Niño–Southern Oscillation (ENSO) in building an anomalous western North Pacific anticyclone (WNPAC) in winter to the succeeding summer. The isolated ENSO and EAWM parts (termed ENSOres and EAWMres, respectively) are acquired by removing the ENSO–EAWM interdependent part through linear regression. The results suggest that both ENSOres and EAWMres can produce a WNPAC in winter. The ENSOres‐related WNPAC dominantly covers the southern part of the western North Pacific, whereas the EAWMres‐related WNPAC over the northern part of the western North Pacific. In the subsequent spring and summer, only ENSOres yields a WNPAC, while EAWMres has no effect on the atmospheric circulation over the western North Pacific. Additionally, the Pacific Decadal Oscillation (PDO) can modulate the influence of ENSOres and EAWMres on the WNPAC. There tends to be a much stronger WNPAC associated with ENSOres (EAWMres) during positive (negative) PDO phases than during negative (positive) ones.