Seasonal Variability of Wintertime Eastern Pacific Teleconnection Pattern and Its Linkage with Tropical Convective Heating

North Pacific teleconnections have a far-reaching impact on weather and climate that spans the North Pacific and surrounding area.  Conventional method for studying teleconnections is EOF analysis, which assumes a teleconnection pattern is a single pattern with fixed center. Using the self-organizing map (SOM) analysis, this study examines the teleconnections of the wintertime North Pacific from a continuum perspective, with a teleconnection pattern consisting of many similar spatially varying patterns. It is found that most of the North Pacific teleconnections can be grouped into several Pacific–North American (PNA)-like, western Pacific (WP)-like, and east Pacific (EP)-like SOM patterns. The eastward seasonal shift of the North Pacific teleconnections could be interpreted as arising from an increase in frequency of EP-like SOM patterns from early to late winter, and vise versa for the WP-like SOM patterns. The EP, which has received little attention before, is found to be associated with statistically significant sea ice cover anomalies over the Sea of Okhotsk and the Bering Sea, as well as precipitation anomalies over the west coast of North America.

The mechanisms of EP formation and its seasonal shift are investigated using daily ERA-Interim data and outgoing long-wave radiation data. It is shown that the formation of the EP is preceded by an anomalous tropical convection dipole, with one extremum located over the eastern Indian Ocean–Maritime Continent and the other over the central Pacific. The tropical convection anomalies excite two quasi-stationary Rossby wave trains: one propagates along the East Asian jet from southern China toward the eastern Pacific; the other propagates northward from east of Japan toward eastern Siberia and then turns southeastward to the Gulf of Alaska. Both wave trains are associated with wave activity flux convergence where the EP pattern develops. The results from an examination of the E vector suggest that the EP undergoes further growth with the aid of positive feedback from high-frequency transient eddies. The frequency of occurrence of the dipole convection anomaly increases significantly from early to late winter, suggesting that the seasonal change in the convection anomaly accounts for the EP being more dominant in late winter.