Climate Dynamics, submitted

The Role of Ocean Dynamics in Producing Decadal Climate Variability in the North Pacific

David W. Pierce, Tim P. Barnett, and Niklas Schneider
Climate Research Division, Scripps Institution of Oceanography

R. Saravanan
National Center for Atmospheric Research, Boulder, CO

Dietmar Dommenget and Mojib Latif
Max Plank Institute for Meteorology, Hamburg, Germany


Decadal time scale climate variability in the North Pacific has implications for climate both locally and over North America. A crucial question is the degree to which this variability arises from coupled ocean/atmosphere interactions over the North Pacific that involve ocean dynamics, as opposed to either purely thermodynamic effects of the oceanic mixed layer integrating in situ the stochastic atmospheric forcing, or the teleconnected response to tropical variability. The part of the variability that is coming from local coupled ocean/atmosphere interactions involving ocean dynamics is potentially predictable by a ocean/atmosphere general circulation model (O/A GCM), and such predictions could (depending on the achievable lead time) have distinct societal benefits. This question is examined using the results of fully coupled O/A GCMs, as well as targeted numerical experiments with stand-alone ocean and atmosphere models individually. It is found that coupled ocean/atmosphere interactions that involve ocean dynamics are important to determining the strength and frequency of a decadal-timescale peak in the spectra of several oceanic variables in the Kuroshio extension region off Japan. Local stochastic atmospheric heat flux forcing, integrated by the oceanic mixed layer into a red spectrum, provides a noise background from which the signal must be extracted. Although teleconnected ENSO responses influence the North Pacific in the 2-7 years/cycle frequency band, it is shown that some decadal-timescale processes in the North Pacific proceed without ENSO. Likewise, although the effects of stochastic atmospheric forcing on ocean dynamics is discernible, a feedback path from the ocean to the atmosphere is indicated by the results. This feedback path is demonstrated to be a sensitivity of the atmospheric wind stress curl field to the pattern of sea surface temperature anomalies in the North Pacific.

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