Date: Monday, December 1, 2008
3:00 pm: Conversation and Cookies in Room 108 Atmospheric Sciences Building
3:30 pm: Seminar in Room 269 Everitt Lab
The leading pattern of extratropical Pacific sea surface temperature variability (the Pacific Decadal Oscillation [PDO]) is shown to depend on observed variability in the spatiotemporal distribution of tropospheric Rossby wave breaking (RWB), where RWB is the irreversible overturning of potential vorticity on isentropic surfaces. Composite analyses based on hundreds of RWB cases show that anticyclonic
(cyclonic) RWB is associated with a warm, moist (cool, dry) column that extends down to a surface anticyclonic (cyclonic) circulation, and that the moisture and temperature advection associated with the surface circulation patterns force turbulent heat flux anomalies that project onto the spatial pattern of the PDO. These results explain the free troposphere-to-surface segment of the atmospheric bridge concept wherein El Nino anomalies emerge in summer and modify circulation patterns that act over several months to force sea surface temperature anomalies in the extratropical Pacific during late winter or early spring. The January PDO index for 1958-2006 is modeled using the leading principal components of cyclonic and anticyclonic RWB from the immediately preceding winter and summer months (four indices in all), accounting for more than two thirds of the variance.
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