Department of Atmopsheric Sciences
University of Illinois
3:00 pm: Conversation and Cookies in Room 108 Atmospheric Sciences Building
3:30 pm: Seminar in Room 114 Transportation Building
The Pacific Decadal Oscillation (PDO) is an ENSO-like climate oscillation that varies on multi-decadal and higher frequency scales, with its centers of action in the North Pacific. Using composite difference fields constructed from the NCEP reanalysis and from CRU, the associated anomalies of the atmospheric fields of 500 mb geopotential height, surface air temperature, sea level pressure, and precipitation are examined. These anomalies vary not only across seasons, but also from one calendar month to another within a season, although month-to-month continuity is apparent. The most significant downstream anomalies occurring in western North America and in the southeastern United States, where a positive PDO is associated with negative height anomalies and temperature anomalies in the winter. In the northwest United States significant anomalies also occur in the summer, with negative height anomalies and positive precipitation anomalies associated with the positive PDO. The seasonality is further investigated by fitting an annual harmonic to the twelve monthly differences at each grid point. An annual cycle in the PDO signal peaks in winter in most of North America, especially along the Western Coast, while a peak in summer occurs in the southeastern United States.
A clearer distinction between the ENSO and PDO signals in the atmosphere is investigated by evaluating a residual PDO signal that is independent of ENSO. Approximately 25% of the variance of the PDO is explained by ENSO. The atmospheric anomalies associated with the residual PDO have many similarities to the full PDO signal.
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