The circularly propagating pattern of the low-frequencyfluctuations of monthly MSL in the tropical PacificOcean and its correlation with El Nino

The long-term time series analysis of the SST (sea surface temperature) in the Eastern Equatorial Pacific Ocean and the monthly MSL (mean sea level) in the tropical Pacific Ocean is conducted. Their quasiperiodic and low-frequency oscillation features are revealed. The significant periods of low-frequency fluctuations for monthly MSL in the area of 20°N-20°S are between 43.5 months and 50.0 months, approximating closely to 47.6 months which is the significant period of SST in the Eastern Equatorial Pacific Ocean. From the results of space-spectral analysis, the low-frequency fluctations of monthly MSL in the tropical Pacific Ocean appear to have a anticlockwise circularly-propagating pattern, which is, the Eastern Pacific Ocean (off-shore of Mexico)→the area of NEC (North Equatorial Current)→the Western Equatorial Pacific Ocean→the area of NECC (North Equatorial Counter-Current)→the Eastern Equatorial Pacific Ocean. The phases of the pattern correspond to those of El Nino cycle. On the basis of the above results,a basic model is established with stepwise-regression method,which can forecast El Nino events by the variations of monthly MSL at a few stations fn the tropical Pacific Ocean 4 months ahead. The correlation inefficient between the forrrnsted series and the nknsrrved one is 0.89.