INTERDECADAL AND INTERANNUAL VARIATIONS OVER THE NORTH PACIFIC SIMULATED BY A SET OF 3 CLIMATE EXPERIMENTS

A set of three climate experiments is performed using a T42 GCM versio n of the Japan Meteorological Agency global model to examine extratrop ical interdecadal and interannual variations over the North Pacific re gion associated with the anomalous SST forcing in the Tropics. Three i ndependent 34-yr integrations from January 1955 to December 1988 are f orced by the same SST boundary condition observed on the global scare. The set of these integrations provides clear evidence that the tropic al SST impact upon the wintertime extratropical model atmosphere in th e North Pacific is very significant. It is also concluded that the abr upt change of midlatitude circulation regime that occurred in the wint er of 1976/77 was primarily caused by very localized tropical heating in the central Pacific. This anomalous SST forcing was most likely res ponsible for persistent negative height anomalies over the central Nor th Pacific during at least the period from 1977 to 1983, which formed a part of the extratropical wave train traversing the North Pacific an d North America, which produced warm temperature anomalies along the w est coast of North America, as well as western Canada. However, an inc rease in observed wintertime surface temperature over northern Eurasia at almost the same period can little be explained by anomalous SST fo rcing from the Tropics. The internal variability of the extratropical atmosphere itself is suggested to contribute much more to the circulat ion regime over the Eurasian continent.