Seasonal Cycle and ENSO

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Seasonal Cycle and ENSO

Is the seasonal cycle necessary for ENSO to be realized? Not likely: Many models without an annually varying sun have proven successful at simulating interannual variability that is ENSO-like. These models include the intermediate coupled numerical atmosphere/ocean models (see, e.g., Suarez and Schopf [1988]; Mantua [1994]) and coupled atmosphere/ocean GCMs [ Latif et al., 1993; Philander et al., 1992]. Is the seasonal cycle fundamental to the irregularity in the ENSO events? All of the aforementioned models are run without an annually varying sun and the ENSO events that they produce occur irregularly. However, ENSO is sufficiently tied to the annual cycle that it is useful to think of a canonical ENSO event, formed by compositing observations fixed to the calendar year [ Rasmusson and Carpenter, 1982].