THE RELATION OF MULTIPLE FLOW REGIMES TO THE CLIMATIC ERROR IN GENERAL-CIRCULATION MODELS - SOUTHERN-HEMISPHERE WINTER

Extended, perpetual July integrations of the NCAR Community Climate Model, versions CCM1 and CCM0, at rhomboidal wavenumber 15 truncation are examined to determine the influence of the models' ability to capture observed planetary-scale flow regimes on their level of climatic error. The Southern Hemisphere (SH) was chosen as the domain of study because the absence of major sources of stationary zonally asymmetric forcing make it a relatively less complicated case compared to the Northern Hemisphere. CCM1 exhibits a distinct deficit in grid point 500 mb height variance and insufficient persistence at large planetary-scale wave amplitude compared to observations or to CCM0. This deficit appears to be connected with the failure of CCM1 to simulate the observed planetary-scale flow regimes in the SH, exemplified in observations as bimodality in the wavenumber 3 amplitude. In particular, CCM1 does not achieve the observed large-amplitude wavenumber 3 regime. On the other hand, CCM0 does capture the wave amplitude bimodality and coincidentally has larger grid point height variance and greater persistence at large amplitude than CCM1. The CCM1 perpetual July SH climate resembles observed SH summer more closely than observed winter in terms of the wavenumber 3 amplitude distribution and the kinetic energy spectrum.