The Observed and Simulated Atmospheric Seasonal Cycle. Part I: Global Wind Field Modes

Abstract

The seasonal cycle of the global wind field is documented for both a decadal set of analyses from the National Meteorological Center (NMC) and an extended term integration of a research version of the Community Climate Model developed at the National Center for Atmospheric Research. Composite eigenvector analysis is used to establish the dominant three dimensional coherent structures characteristic of the datasets while gridpoint harmonic analysis provides evidence of the extent to which these structures describe conventional seasonal modes. These quantitative indicators of spatial and temporal variance form a stringent measure of model performance with respect to seasonal variation. The model appears to be far more successful at capturing the annual harmonic contained in the NMC analyses than the semiannual harmonic. This discrepancy may be related to the absence of the requisite tropical forcings due to either inadequate parameterizations of certain physical processes or the lack of interannual variability in the model's boundary forcings, or both. Further numerical experimentation is likely to help resolve this issue.