The Relationship between the Asian/Australian Monsoon and ENSO on a Quasi-Four-Year Scale

The interannual variability of tropical zonal wind and the relationship between ENSO and the Asian/Australian monsoon in different phases are discussed. Results show that the tropical zonal wind strongly couples with the central-eastern Pacific SST on a quasi-four-year scale. During the period of El Nino, the East Asian winter (summer) monsoon is weaker (stronger) and the South Asian summer monsoon is weaker than normal. Conversely, the East Asian winter (summer) monsoon is stronger (weaker) and the South Asian summer monsoon is stronger than normal during the period of La Nina. The anomalous northerly over East Asia induces an anomalous westerly over the western equatorial Pacific, which favors the appearance of positive SST anomalies in the central-eastern Pacific. The development of El Nino requires the persistence of a westerly over the central-eastern Pacific. The convergence between anomalous northerlies from the central North Pacific (not from the East Asian continent) and anomalous southerlies from Northeast Australia favors the persistence of a westerly over the central-eastern Pacific. In particular, the anomalous southerlies from Northeast Australia play a key role in the onset of strong westerly anomalies over the tropical central-eastern Pacific.