A FURTHER INQUIRY ON ESSENCE OF THE ENSO CYCLE

Based on scientific theory-the ENSO results from air sea interaction in the tropical Pacific, the analyses and CGCM simulation showed that there is interaction between the ENSO and anomalous East Asian winter monsoon, the continued strong (weak) East Asian winter monsoon plays an important role in the occurrence of El Nio (La Nia) through causing the westerly (easterly) wind anomalies over the equatorial western Pacific; the ENSO is closely related to the subsurface ocean temperature anomalies (SOTA) in the western Pacific warm pool and its evolution. There is always positive (negative) SOTA in the warm pool region prior to the occurrence of El Nio (La Nia) event, but after the occurrence of El Nio (La Nia), there is negative (positive) SOTA. The precedence of ENSO is exactly in the western Pacific warm pool and the occurrence of ENSO is directly related to the SOTA in the warm pool and its eastward propagation along the equatorial thermocline. The SOTA in the tropical Pacific has very clear interannual cycle. The cycle consists of eastward propagating positive SOTA along the equator and the associated westward propagation of negative SOTA along 10°N and 10°S latitudes; then the eastward propagation of negative SOTA along the equator is also associated to the westward propagation of positive SOTA along 10°N and 10°S latitudes. The analyses still show that the eastward propagation of SOTA along the equator is directly related to anomalous zonal wind over the equatorial western Pacific, which is mainly caused by anomalous East Asian winter monsoon. Therefore, it can be suggested that the atmospheric circulation anomaly in the middle latitude, particularly the anomaly of winter monsoon in East Asia, plays an important role in the ENSO occurrence; i.e., the ENSO is exactly the cycle of subsurface ocean temperature anomalies in the tropical Pacific driven by anomalous zonal wind over the equatorial western Pacific caused mainly by anomalous East Asian monsoon.