Principal components of the monthly global analyses of sea surface temperatures (SSTs) for the period of 1955-1993 are utilized to study the large-scale modes of SST variations in association with the variability and predictability of atmospheric circulation. The first and second components of the SST field well describe the occurrence of El Nino episodes in terms of the El Nino index (ENI), which is defined as the weighted mean of the coefficients of the first and second components. The coupling modes of the ocean-atmospheric system are examined by correlation analysis of the principal components of SSRs and those of upper-air circulation fields. The El Nino mode strongly influences the winter troposheric circulation in the middle latitudes for up to three leading seasons. A possible utilization of the ENI in the seasonal-range projection of atmospheric circulation is indicated by the cross-correlation between the preceding ENIs and the following troposheric circulation for both winter and summer circulation. For the dominance of the El Nino type anomaly fields in the past decade, the principal components of SSTs during the period of July 1991 to December 1003 are also presented.
The feasibility of local long-range forecasting is explored in association with SST anomalies for Taiwan Mei-Yu and for monthly temperature and precipitation over the United States. For Taiwan Mei-Yu, in utilizing the useful complimentary characteristics of the winter El Nino mode and residual components of SST anomalies, the possibility of regional recasting is exam ined. For the U.S. climatological stations, teleconnections between principal components of SSTs and monthly temperature and precipitation indicate the usefulness of the former as predictors.