EOF analysis has been conducted of the interdecadal variability of sea temperature anomaly fields at standard levels in the subsurface, and the abrupt change feature of sea temperature has been tested by use of movable t-test technique. A possible mechanism of the ocean-air system in the tropical Pacific is investigated by using the subsurface temperature, heat storage and wind stress data, leading to the main results as follows.
The analysis indicates that around 1980 there occurs a significant interdecadal abrupt change of temperature from sea surface to different depths, of which 4 modes show the accident and their formation is closely related to the southwestward subduction route of North Pacific sea temperature anomalies. The interdecadal signal of subduction in the window region of the North Pacific propagates southwestward to the subtropics, meeting the anomalous signal which propagates northeastward from the western Pacific at ~ 160-meter level in the thermocline. Therefore, the influence of the former on ENSO interdecadal variability might be indirect while the latter plays a more important role.
The western tropical South Pacific, which displays evident interdecadal variability, is the key region of the ENSO interdecadal variability. The positive temperature anomaly will move to the mid-tropical Pacific and the atmospheric response will excite an anticyclonic wind stress to the east of Australia, which will lead to the generation of a negative temperature anomaly in the tropical southwest Pacific. A similar evolution with an opposite sign will follow subsequently. The whole cycle takes about 13 years to complete.