Predictability of a Coupled Model of ENSO Using Singular Vector Analysis. Part I: Optimal Growth in Seasonal Background and ENSO Cycles

The fastest initial error growth (optimal growth) in the Zebiak and Cane (ZC) forecast model for the El Nin o-Southern Oscillation (ENSO) is analyzed by singular value decomposition of a forward tangent model along a trajectory in a reduced EOF space. In this paper (Part I of II), optimal growth about the seasonally varying background and ENSO cycles from a long model run are discussed.