DECADAL ATMOSPHERE-OCEAN VARIATIONS IN THE PACIFIC

Considerable evidence has emerged of a substantial decade-long change in the north Pacific atmosphere and ocean lasting from about 1976 to 1 988. Observed significant changes in the atmospheric circulation throu ghout the troposphere revealed a deeper and eastward shifted Aleutian low pressure system in the winter half year which advected warmer and moister air along the west coast of North America and into Alaska and colder air over the north Pacific. Consequently, there were increases in temperatures and sea surface temperatures (SSTs) along the west coa st of North America and Alaska but decreases in SSTs over the central north Pacific, as well as changes in coastal rainfall and streamflow, and decreases in sea ice in the Bering Sea. Associated changes occurre d in the surface wind stress, and, by inference, in the Sverdrup trans port in the north Pacific Ocean. Changes in the monthly mean flow were accompanied by a southward shift in the storm tracks and associated s ynoptic eddy activity and in the surface ocean sensible and latent hea t fluxes. In addition to the changes in the physical environment, the deeper Aleutian low increased the nutrient supply as seen through incr eases in total chlorophyll in the water column, phytoplankton and zoop lankton. These changes, along with the altered ocean currents and temp eratures, changed the migration patterns and increased the stock of ma ny fish species. A north Pacific (NP) index is defined to measure the decadal variations, and the temporal variability of the index is explo red on daily, annual, interannual and decadal time scales. The dominan t atmosphere-ocean relation in the north Pacific is one where atmosphe ric changes lead SSTs by one to two months. However, strong ties are r evealed with events in the tropical Pacific, with changes in tropical Pacific SSFs leading SSTs in the north Pacific by three months. Change s in the storm tracks in the north Pacific help to reinforce and maint ain the anomalous circulation in the upper troposphere. A hypothesis i s put forward outlining the tropical and extratropical realtionships w hich stresses the role of tropical forcing but with important feedback s in the extratropics that serve to emphasize the decadal relative to interannual time scales. The Pacific decadal timescale variations are linked to recent changes in the frequency and intensity of El Nino ver sus La Nina events but whether climate change associated with ''global warming'' is a factor is an open question.