Abstract
The seasonal interactions between mid-latitude circulation patterns and the first two dominant sea surface temperature (SST) anomaly patterns over the North Pacific were statistically analyzed. The first SST mode contributes to the formation and evolution of the Pacific/North American (PNA) pattern during wintertime. In contrast, the second SST mode is partly formed by the cold surge from the East Asia during wintertime closely associated with the dominance of low index circulation. When this mode is dominant, the Western Pacific (WP) pattern is prominent at the 500mb height field. Further this mode is also influenced by the outbreak of polar cold air which is accumulated in early summer and released toward the East Asia in mid-summer. In the middle latitudes the negative SST anomalies of the first mode at about 40°N are mainly formed by mechanical forcing of the atmosphere and the negative SST anomalies of the second mode over the western Pacific are formed by thermal forcing (cold surge) of the atmosphere.
