A Data Analysis Study on the Evolution of the EI Ni?o/ La Ni?a Cycle

The curved surface of the maximum sea temperature anomaly (MSTA) was created from the JEDACsubsurface sea temperature anomaly data at the tropical Pacific between 1955 and 2000. It is quite similar tothe depth distribution of the 20°C isotherm, which is usually the replacement of thermocline. From the dis-tribution and moving trajectory of positive or negative sea temperature anomalies (STA) on the curved sur-face we analyzed all the El Nino and La Nina events since the later 1960s. Based on the analyses we foundthat, using the subsurface warm pool as the beginning point, the warm or cold signal propagates initiallyeastward and upward along the equatorial curved surface of MSTA to the eastern Pacific and stays thereseveral months and then to turn north, usually moving westward near 10°N to western Pacific and finallypropagates southward to return to warm pool to form an off-equator closed circuil. It takes about 2 to 4years for the temperature anomaly to move around the cycle. If the STA of warm (cold) water is strongenough, there will be two successive El Nino (La Nina) events during the period of 2 to 4 years. Sometime, itbecomes weak in motion due to the unsuitable oceanic or atmospheric condition. This kind process may notbe considered as an El Nino ( La Nina) event, but the moving trajectory of warm (cold) water can still berecognized. 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 near10 N in eastern Pacific before the outbreak of El Nino (La Nina) event. The signals move in the opposite di-rections. So it appears as El Nino (La Nina) in equator at 2-4 years intervals. The paper also analyzed sev-eral exceptional cases and discussed the effect and importance of oceanic circulation in the evolution of ElNino/La Nina event.