Analysis of a Conceptual Model of Seasonal Climate Variability and Implications for Seasonal Prediction

Abstract

Abstract A thought experiment on atmospheric interannual variability associated with El Nino is formulated and is used to investigate the seasonal predictability as it relates to the practice of generating ensemble GCM predictions. The purpose of the study is to gain insight on two important issues within seasonal climate forecasting: (i) the dependence of seasonal forecast skill on a GCM's ensemble size, and the benefits to be expected from using increasingly larger ensembles, and (ii) the merits of dynamical GCM techniques relative to empirical statistical ones for making seasonal forecasts, and the scenarios under which the former may be the superior tool. It is first emphasized that seasonal predictability is an intrinsic property of the observed system, and is inherently limited owing to the nonzero spread of seasonally averaged atmospheric states subjected to identical SST boundary forcing. Further, such boundary forced predictability can be diagnosed from the change in the statistical distribution ...