Estimates of First- and Second-Moment Climate Statistics in GCM Simulated Climate Ensembles

Abstract

Traditionally the climate simulated by an atmospheric general circulation model (GCM) has been presented in terms of individual monthly or seasonal averages from a single realization. A more complete description of GCM simulated climate is possible by means of sampled climate ensembles consisting of sets of independent, finite time-span realizations. As an example of this sampled climate ensemble approach, estimates of first- and second-moment climate statistics are presented for grid-point data from GCM simulated climate ensembles produced by perpetual January and July versions of a 2.5° horizontal resolution GCM developed several years ago at the National Center for Atmospheric Research. Estimates of ensemble averages and standard deviations are included for time averages and for time-lagged autocorrelations for several different lags. Also included as an integral measure of persistence for these same sampled ensembles are estimates of the characteristic time (T₀) between effectively independent sample values.