It is a pleasure to acknowledge many useful discussions with Eric Simonnet, Niklas Schneider, and the constructive comments of two anonymous referees. The SODA data were obtained via the IRI/LDEO Climate Data Library (http://iridl.ldeo.columbia.edu/). Many of the spectral analyses were carried out using the SSA-MTM Toolkit for Spectral Analysis (http://www.atmos.ucla.edu/tcd/ssa/). This work was supported by U.S. Department of Energy grants DE-FG02-02ER63413 and DE-FG02-07ER64439 at UCLA and DE-FG02-07ER64429 at the IRI.
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