Response of a GFDL General Circulation model to sst Fluctuations Observed in the Tropical Pacific Ocean During the Period 1962–1976

The results of a special 15-year integration of an atmospheric general circulation model are compared with observations. In the 30°S-30°N strip over the Pacific, the lower boundary of the model is forced by sea-surface temperatures which vary continuously according to actual observations during the period January 1962-December 1976. Everywhere else, the sea-surface temperatures follow a normal annual cycle without year-to-year variations. Using global telecon-nection maps and time series of certain tropical circulation indices, such as the low-level and upper-level zonal winds, the surface pressure and the 200-mb height, it is shown that the dominant spatial modes of atmospheric variability in the tropics are very well simulated. Some of these modes are conspicuously absent from an earlier integration in which the surface temperatures everywhere were prescribed to follow the normal seasonal cycle.