Interdecadal and Interannual Variations over the North Pacific Simulated by a Set of Three Climate Experiments

Abstract

A set of three climate experiments is performed using a T42 GCM version of the Japan Meteorological Agency global model to examine extratropical interdecadal and interannual variations over the North Pacific region associated with the anomalous SST forcing in the Tropics. Three independent 34-yr integrations from January 1955 to December 1988 are forced by the same SST boundary condition observed on the global scale. The set of these integrations provides clear evidence that the tropical SST impact upon the wintertime extratropical model atmosphere in the North Pacific is very significant. It is also concluded that the abrupt change of midlatitude circulation regime that occurred in the winter of 1976/77 was primarily caused by very localized tropical heating in the central Pacific. This anomalous SST forcing was most likely responsible for persistent negative height anomalies over the central North Pacific during at least the period from 1977 to 1983, which formed a part of the extratropical wave train traversing the North Pacific and North America, which produced warm temperature anomalies along the west coast of North America, as well as western Canada. However, an increase in observed wintertime surface temperature over northern Eurasia at almost the same period can little be explained by anomalous SST forcing from the Tropics. The internal variability of the extratropical atmosphere itself is suggested to contribute much more to the circulation regime over the Eurasian continent.