Distinguishing Between the Atmospheric Response to the Variability of the Kuroshio and the Oyashio Extensions in the Cold Season and the Impact of the Main Extratropical and Tropical SST Modes, and Sea-Ice Concentration Changes

The variability of the Oyashio and the Kuroshio Extensions is associated with large SST changes in the Kuroshio-Oyashio Extension region that show some similarity with the Pacific Decadal Oscillation (PDO). In order to compare their influence on the cold season atmospheric circulation with that of the tropical SST variability and other main modes of boundary forcing, a multiple regression analysis is performed, using observational or reanalysis datasets in the 1979-2014 period. It is shown that, despite the strong influence of the tropical SST, the influences of the meridional shifts of the Oyashio Extension and of the change of state of the Kuroshio Extension that were found in simpler analyses is recovered, although statistical significance can be lower, and there are differences between early and late winter. Nonetheless, the influence of the Kuroshio and Oyashio Extensions can largely be distinguished from the impact of the PDO, the North Pacific gyre mode, and sea ice changes in the North Pacific.