Deterministic and statistical properties of the Westerlies

A brief description is presented of the classical theory of middle-latitude atmospheric circulation, which is essentially based on the analysis of zonally averaged stationary flows and their stability properties. The structure and the statistical properties of observed circulation are discussed in some detail. Particular emphasis is placed upon the long-lasting anomalies usually associated with the meteorological phenomenon of “blocking.” Anomalies raise several physical interpretations that may be keys to understanding the statistical properties of the atmospheric system and therefore of climate. Recent developments in the study of global properties of the phase space of simplified theoretical prototypes of atmospheric circulation are then described. Problems to be solved in the future are emphasized. Stability properties of zonally nonsymmetric circulations in the presence of global-scale topographic reliefs are discussed, showing that the solutions of some of the outstanding physical problems in the theory of atmospheric circulation may be found in the analysis of local properties of the phase space of model atmospheres. Although the recent application to meteorology of techniques of analysis of strongly nonlinear systems has produced results of extreme interest, the general conclusion is drawn that much can still be learned by means of the classical instruments of theoretical meteorology