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Seminar Abstract

Mike Wallace, Craig Brown, & Nate Mantua - Dec 4, 2001

Extreme PNW weather events and their relationships with the Arctic Oscillation and Pacific North America circulation patterns

While seasonal mean PNW climate variations have been documented and related to indices tracking large scale patterns in the climate system, little work has focused on better understanding the statistics of extreme (daily time scale) PNW weather events. In this talk, we report on the results of studies aimed at documenting and describing connections between extreme weather events and two large scale circulation patterns, the Arctic Oscillation (AO) and the Pacific North America (PNA) pattern. Variability in the AO and PNA patterns explain a sizeable fraction of the seasonal as well as within season variability in North American surface climate. In our work we quantify relationships between AO, PNA and statistics of extreme PNW weather events. Previous studies have documented clear relationships between variations in the AO and extremely high and low temperature days in many parts of the US, including the PNW. Preliminary results of this study show relatively large differences in the statistics of extremely cold and warm PNW days observed during positive and negative periods of the PNA pattern. Because the statistics of the PNA circulation pattern differ during different eras of the Pacific Decadal Oscillation (PDO) and ENSO, this work provides evidence that the causal chain linking ENSO and PDO to the statistics of regional climate includes changes in the statistics of daily hemispheric-scale circulation patterns.

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