Global Distribution of Vertically-Averaged Meridional Momentum Transport Statistics for January: A Comparison between Observations and General Circulation Model Simulations

Abstract

Abstract Vertically-averaged meridional transports of westerly momentum are analyzed in sampled ensembles of January simulations of an NCAR GCM and an equivalent ensemble of five years of observational January data according to a simple time-domain decomposition. Ensemble averages and standard deviations are compared in terms of both zonally-averaged and grid-point presentations for the steady and transient flux components highlighting the relative characteristics of the fundamental time-domain elements. Results from 5 and 2.5° horizontal resolution versions of the model demonstrate the impact of truncation error on model simulations of these flux statistics. Comparing grid point measures constitutes a more stringent model performance evaluation since regional differences between observed and simulated transports often are found to he considerably larger than zonally-averaged differences. Such regional considerations also reveal substantial differences between model and observations in the location and or...