THE STATISTICAL PROPERTIES OF GENERAL ATMOSPHERIC CIRCULATION - OBSERVATIONAL EVIDENCE AND A MINIMAL THEORY OF BIMODALITY

After a brief re-examination of the Charney-DeVore theory of multiple equilibria, we compare the statistical properties that can be deduced from it with those resulting from analysis of observations of the northern hemisphere middle-latitude circulation at 500 mb. While the prediction concerning the amplitude of the waves seems to be confirmed by the presence of a clear bimodality of the statistical distribution, we find no trace of bimodality in the zonal wind. We show how the theory can be brought into agreement with observations by introducing nonlinearity into the wave equation in such a way that the Charney-DeVore resonance curve is bent, producing different states corresponding to the same value of the zonal wind