Data Analyses On The Tropical Pacific And Indian Ocean Air-Sea Interaction Events

The surface of the maximum sea temperature anomaly(MSTA) was constructed from the subsurface sea temperature anomaly data in the tropical Pacific from 1955 to 2002. It is quite similar to the depth distribution of the 20?C isotherm, which is usually used to represent the center of the thermocline layer. From the distribution and moving trajectory of positive or negative sea temperature anomalies(SMTA) on the surface, the 1997-1998 El Nino event was studied first and then all the El Nino and La Nina events since the later 1960s were analyzed. Based on the analyses, it was found that if the subsurface warm pool is regarded as the beginning point, the warm or cold signal propagates initially eastward and upward along the equatorial surface of MSTA to the eastern Pacific and stays there several months and then turns north, usually moves westward near 10 to western Pacific and finally propagates southward to return to warm pool to form an off-equator closed circuit. It takes about 2 to 4 years for the temperature anomaly to move around the cycle. If the SMTA of warm(cold) water is strong enough, there will be two successive El Nino(La Nina) events during the period of 2 to 4 years. Sometimes it becomes weak in motion due to the unsuitable oceanic or atmospheric condition. This kind process may not be considered as an El Nino(La Nina) event, but the moving trajectory of warm(cold) water can still be recognized. Because of the alternate between warm and cold water around the circuits, the positive(negative) anomaly signal in equatorial western Pacific coexists with negative(positive) anomaly signal near 10 in eastern Pacific before the burst of El Nino(La Nina) event. The signals move in the opposite directions. So it appears as El Nino(La Nina) in equator at 2 to 4 years intervals. The paper also analyzed several exceptional cases and discussed the effect and importance of oceanic circulation in the evolution of El Nino(La Nina) event.Furthermore, analysis on the relation between the local wind stress curl anomalies(WSCA) and SMTA shows that WSCA plays different roles on SMTA dueto its different variances. There exists strong correlation between them in those regions with large variance of WSCA, and the change of WSCA precedes that of SMTA. The analysis also shows that WSCA mainly affects SMTA by changing the depth of the Thermocline. The spectral analysis on the WSCA of the North-West Pacific(140 E-180 ,8 N-15 N) indicates that its main period is from 3 to 5 years, which is almost the same as that of SMTA in Nino 3 zone. That's to say that this region in some sense is the dynamical source in the atmosphere driving the development of El Nino event.On the surface of MSTA, there exists true Dipole Mode in the Indian Ocean, that's to say that if the temperature anomaly in the western Indian Ocean is positive, it is much likely that there is negative anomaly in the eastern Indian Ocean. Dipole Mode also exists in the Pacific as that in the Indian Ocean. By virtue of the Walker circulation and the similar circulation above the Indian Ocean, it is showed that the air-sea interaction events in the tropical Pacific and the Indian Ocean develop with each other at the same time.