ON THE CLIMATOLOGY OF PERSISTENT CIRCULATION ANOMALIES IN THE ATMOSPHERE AND IN A GENERAL-CIRCULATION MODEL

The climatologies of upper-air persistent circulation anomalies found in observations of the Northern Hemisphere and in a General Circulation Model (GCM) integration are compared with each other and with those found in previous studies. The model simulation is that of the Canadian Climate Centre GCM run at resolution T20. The objective criteria that define the persistent events differ rom those of some earlier investigations in that the anomalies are not required to be as nearly stationary. It is found that the GCM generates persistent circulation anomalies downstream of the synoptic-scale storm tracks, in very nearly the correct geographical locations, but that the frequency of occurrence is too low in the model. A kinetic energy and streamfunction variance analysis is presented for both datasets to clarify the differences between the observed and simulated distributions of circulation anomalies. It is evident that, apart from the mean annual cycle, the middle-latitude transient eddies of the model are too weak.