The Principal Nonseasonal Modes of Variation of Global Sea Surface Temperature

Thirty-five million ship reports for the period 1949–79 have been used to construct global, monthly-mean sea surface temperature fields for 5° × 5° latitude-longitude regions. The monthly means have been subjected to eigenvector analysis to bring out the nonseasonal modes of variation. The El Niño mode is the most important and its eigenvector time series is identical to that found previously by Weare et al. for the Pacific alone. Addition of data from the other oceans adds unexplained variance so that the percentage of the variance explained by the El Niño mode is smaller in the global case than for the Pacific alone. The second most important eigenvector pattern shows evidence of a cooling trend for the North Pacific and North Atlantic in the 1964–79 period. This is in agreement with previous work an zonal-mean sea surface temperature by the authors, with recent work on the North Pacific by Douglas et al. and with a polar-cap cooling in the lower troposphere for the same period reported by Boer and Higuchi.