TRENDS, INTERDECADAL AND INTERANNUAL OSCILLATIONS IN GLOBAL SEA-SURFACE TEMPERATURES

This study aims at a global description of climatic phenomena that exh ibit some regularity during the twentieth century. Multi-channel singu lar spectrum analysis is used to extract long-term trends and quasi-re gular oscillations of global sea-surface temperature (SST) fields sinc e 1901. Regional analyses are also performed on the Pacific, (Northern and Southern) Atlantic, and Indian Ocean basins. The strongest climat ic signal is the irregular long-term trend, characterized by overall w arming during 1910-1940 and since 1975, with cooling (especially of th e Northern Hemisphere) between these two warming intervals. Substantia l cooling prevailed in the North Pacific between 1950 and 1980, and co ntinues in the North Atlantic today. Both cooling and warming are prec eded by SST anomalies of the same sign in the subpolar North Atlantic. Near-decadal oscillations are present primarily over the North Atlant ic, but also over the South Atlantic and the Indian Ocean. A 13-15-y o scillation exhibits a seesaw pattern between the Gulf-Stream region an d the North-Atlantic Drift and affects also the tropical Atlantic. Ano ther 7-8-y oscillation involves the entire double-gyre circulation of the North Atlantic, being mostly of one sign across the basin, with a minor maximum of opposite sign in the subpolar gyre and the major maxi mum in the northwestern part of the subtropical gyre. Three distinct i nterannual signals are found, with periods of about 60-65, 45 and 24-3 0 months. All three are strongest in the tropical Eastern Pacific. The first two extend throughout the whole Pacific and still exhibit some consistent, albeit weak, patterns in other ocean basins. The latter is weaker overall and has no consistent signature outside the Pacific. T he 60-month oscillation obtains primarily before the 1960s and the 45- month oscillation afterwards.