Interdecadal variation characteristics of winter North Pacific storm tracks and its possible influencing mechanism.

The temporal and spatial characteristics of winter storm tracks in the North Pacific are analyzed on the interdecadal scale by using harmonious wave analysis and EOF analysis method based on the ERA40 data (1958-2002). The influencing mechanism is also discussed through regression analysis with atmospheric circulation and sea surface temperature anomalies as a regressor. The results show that there are two main interdecadal scale variation modes of the storm tracks in the North Pacific during winter. The first mode depicts the variation of storm track against its climatological position, relating to the impact of the remote eddy forcing anomaly over the Atlantic area. The stronger (weaker) Atlantic eddy activity may cause the winter North Pacific westerly jet to become weaker (stronger), broader (narrower) and more northward (southward) and thus cause stronger (weaker) Pacific storm activities as well as a response of local warmer (cooler) SST over the Kuroshio current extension. The second mode depicts a meridional seesaw variation over the storm track, which is associated with the influence of the Pacific Decadal Oscillation (PDO) modes. The surface diabetic heat forcing may enhance (reduce) the PNAlike teleconnection pattern response in 500 hPa height field, cause more baroclinicity abnormally to the south (north), and thus lead the storm track to wholly shifting southard (northward) with its eastern part to migrating to a southern location so that the track appears sloping toward the southeast (northeast). Therefore, the Pacific storm track variations on the interdecadal scale are not only caused by the local eddyzonal mean flow interaction, but also by the remote eddy forcing and diabetic heating effect of SST.