The Pacific Decadal Oscillation, Revisited

Matthew Newman, University of Colorado at Boulder, Boulder, CO, United States, Arthur J Miller, University of California San Diego, La Jolla, CA, United States, Michael A Alexander, NOAA Earth System Research Laboratory, Denver, CO, United States, Toby Ault, Cornell University, Department of Earth and Atmospheric Science, Ithaca, NY, United States, Kim M Cobb, Georgia Institute of Technology Main Campus, Earth and Atmospheric Sciences, Atlanta, GA, United States, Clara Deser, National Center for Atmospheric Research, Boulder, CO, United States, Emanuele Di Lorenzo, Georgia Institute of Technology Main Campus, Program in Ocean Science & Engineering, Atlanta, GA, United States, Nathan J Mantua, NOAA Southwest Fisheries Science Center, Fisheries Ecology Division, La Jolla, CA, United States, Shoshiro Minobe, Hokkaido University, Sapporo, Japan, Hisashi Nakamura, University of Tokyo, Bunkyo-ku, Japan, Niklas Schneider, University of Hawaii at Manoa, Honolulu, HI, United States, Daniel Vimont, University of Wisconsin Madison, Madison, WI, United States, Adam Phillips, NCAR, Boulder, CO, United States, Catherine Anne Smith, NOAA Earth System Research Laboratory, Boulder, CO, United States and James D Scott, Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States
Abstract:
Since its identification in the late 1990’s as the dominant pattern of North Pacific sea surface temperature (SST) variability, the Pacific decadal oscillation (PDO) has been connected both to other parts of the climate system and to impacts on natural resources and marine and terrestrial ecosystems. Variability associated with the PDO has often been confused with externally forced climate change including anthropogenic effects. Subsequent research, however, has found that the PDO is not a single physical mode of climate variability but instead largely represents the combination of three groups of processes: (1) changes in ocean surface heat fluxes and Ekman (wind-driven) transport related to the Aleutian low, due to both local, rapidly decorrelating, unpredictable weather noise and to remote forcing from interannual to decadal tropical variability (largely El Nino) via the “atmospheric bridge”; (2) ocean memory, or processes determining oceanic thermal inertia including “re-emergence” and oceanic Rossby waves, that act to integrate this forcing and thus generate added PDO variability on decadal time scales; and (3) decadal changes in the Kuroshio-Oyashio current system forced by the multi-year history of basin-wide Ekman pumping, manifested as SST anomalies along the subarctic front at about 40N in the western Pacific ocean. Thus, the PDO represents the effects of different processes operating on different timescales, with few of its apparent impacts due to extratropical SST anomalies. This talk presents a synthesis of this current view of the PDO, and discusses corresponding implications for climate diagnosis, including of PDO climate impacts and predictability (both oceanographic and atmospheric); potential decadal regime-like behavior; simulations of the PDO in climate models; the interpretation of paleoclimate multicentennial reconstructions of the PDO; and its impacts on marine ecosystems. We conclude with some suggested “best practices” for future PDO diagnosis and forecasts including investigating the potential role of the PDO in the global temperature hiatus.
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