Pacific Interannual and Interdecadal Equatorial Variability in a 1000-Yr Simulation of the CSIRO Coupled General Circulation Model*

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Abstract The structure and evolution of, and the mechanisms responsible for, interannual and decadal equatorial variability in a 1000-yr simulation of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) coupled general circulation model are examined. Principal component analysis is applied to the 0–270-m integrated heat content from the model to determine dominant modes of variability. The leading mode of unfiltered variability (annual) is best described by an AR2 null hypothesis with an implied periodic timescale of 6–10 yr. Spatial structures of the leading empirical modes of interannual (10-yr high-pass filtered) and decadal (9-yr low-pass filtered) variability closely resemble observations of interannual ENSO, and decadal ENSO-like variability. The amplitude of tropical SST anomalies is too small by a factor of 2–3 on interannual timescales, but is close to that observed for decadal timescales. For interannual timescales, an equatorial heat budget analysis shows a positive feedbac...