The storm track variations in the North Pacific in winter are investigated by using European ECMWF (ERA40) reanalysis data and the Empirical Orthogonal Function (EOF) method. The coupled patterns of the atmosphere mean flow anomaly and the sea surface temperature (SST) anomaly, related with the storm track variations are studied by the regression method. The results show that there are two main variation modes of the storm track in the North Pacific in winter. The first type is characterized by north (south) shift of the mid-east part of the storm track that connotes a northeastward (southeastward) reorientation of the track. The regression analysis shows that the warmer (colder) SSTA occurs in conjunction with antlicyclonic anomalies above that cover the midlatitude North Pacific, companying with the first mode of the storm track. Those are warm ridge (cold trough) pattern in the vertical for the atmosphere-ocean system. Meanwhile, it is Pacific-North American (PNA) negative (positive) phase at the mid and high troposphere. The second type is the intensification (weakening) and northward (southward) shift of the whole storm track. It is associated with warmer (colder) SST in the Kuroshio Current, northward ( southward) shift of the Aleutian Low at the low troposphere and westerly jet at the high troposphere, and Western Pacific (WP) negative (positive) phase at the mid-high troposphere. The time coefficients of EOF have significant correlation with Aleutian Low index, PNA index, WP index, Nino-3 index and the Kuroshio Current index, respectively, which demonstrate the existence of the coupling among the three selected fields.
