The Pacific Decadal Oscillation, air-sea interaction and central north Pacific winter atmospheric regimes

Prominent and persistent anomalies in the atmospheric flow (troughs and ridges) occur sporadically over the central North Pacific, and can have profound consequences for the weather of North America. We have examined how these events are associated with large scale central North Pacific sea surface temperature (SST) anomalies, using an index for the Pacific Decadal Oscillation (PDO). The anomalies in turbulent air-sea heat fluxes and low-level baroclinity associated with the PDO are manifested differently during troughs than during ridges in their effects on the transient eddies (storms). These effects may help explain why prominent troughs (ridges) occur about 3 (2.5) times more frequently during periods when the PDO is significantly positive (negative) than of opposite sign. Our results suggest that the state of the mid-latitude Pacific Ocean more fundamentally affects the atmosphere than has been thought.