Ocean Data Assimilation, Initialization, and Predictions of ENSO with a Coupled GCM

Abstract

A scheme for making seasonal to interannual predictions of El Niño?Southern Oscillation with a coupled atmosphere?ocean general circulation model that incorporates subsurface ocean measurements in the initial conditions is described. Anomaly initial conditions are used in order to reduce initial shock and climate drift. The ocean component of the prediction model has a nearly global domain, and the coupled model does not employ anomaly coupling or empirical statistical corrections. Initial conditions for the ocean were obtained from a near-global ocean analysis produced by an ocean data assimilation system. The assimilation system uses a variationally formulated optimal interpolation method to analyze oceanic fields from temperature observations and a first-guess field provided by integrating a global ocean general circulation model. The period of the analysis was 1986 through 1992. The anomaly initial conditions for the ocean were generated by adding the anomalies of the assimilated fields from the assimilation climatology to the coupled model climatology. A series of 28 1-yr hindcast experiments, four each year for the years 1986?1992, was carried out to test the scheme. The hindcasts show considerable skill in the equatorial Pacific.