Observed Interaction between Pacific Sea Ice and the Western Pacific Pattern on Intraseasonal Time Scales

The relationship between North Pacific sea ice and the Western Pacific (WP) pattern is examined using wintertime observational data between 1978 and 2008. Weekly averaged data are chosen to capture the characteristically short time scale of the WP. A clear relationship is found between the WP and sea ice concentrations in the Bering Sea, where the positive polarity of the WP is accompanied by increasing sea ice concentrations and the negative WP by decreasing sea ice concentrations. Sea ice concentrations in the Sea of Okhotsk, however, are shown to be largely insensitive to the strength of the WP. Feedback of Bering Sea sea ice concentrations onto the WP is tested by fitting weekly averaged observations to a vector autoregressive (VAR) model. Results from the VAR model indicate that feedback of Bering Sea sea ice onto the WP plays a significant role in the dynamics of the WP and that this feedback is positive; that is, WP-induced changes in Bering Sea sea ice concentrations help sustain existing WP conditions, thereby lengthening the time scale of variability of the WP.