| The changes in East Asian winter monsoon (EAWM) associated with the combined effect of
El Niño and Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) are
investigated using various observational datasets. Author argues that when the ENSO and
PDO are in in-phase combination (i.e., El Niño/high PDO phase or La Niña/low PDO phase),
the EAWM tends to be significantly stronger or weaker. However, when the ENSO and PDO
are in out-of-phase combination (i.e., El Niño/low PDO phase or La Niña/high PDO
phase), the EAWM does not exhibit distinct features. Hence, the relationship between
EAWM and ENSO on the interannual timescale is clearly modulated by interdecadal
variations of the PDO, showing a synergistic or dissipative force in accordance with the
phase interferences of ENSO and PDO. The plausible dynamical processes through
which the EAWM is weakened or strengthened is closely linked to the sea surface
temperature response over the confined Western North Pacific region (15-40N,
120-160E) and northeasterly wind anomalies over the central eastern North Pacific
induced by the intensity of Aleutian low and Western North Pacific subtropical
high. |