Maximum Entropy Production and Non-Gaussian Climate Variability

Abstract: Earth's atmosphere is in a state far from thermodynamic equilibrium. For example, the large scale equator-to-pole temperature gradient is maintained by tropical heating, polar cooling, and a midlatitude meridional eddy heat flux predominantly driven by baroclinically unstable weather systems. Based on basic thermodynamic principles, it can be shown that the meridional heat flux, in combination with the meridional temperature gradient, acts to maximize entropy production of the atmosphere. In fact, maximum entropy production (MEP) has been successfully used to explain the observed mean state of the atmosphere and other components of the climate system. However, one important feature of the large scale atmospheric circulation is its often non-Gaussian variability about the mean. This paper presents theoretical and observational evidence that some processes in the midlatitude atmosphere are significantly non-Gaussian to maximize entropy production. First, after introducing the basic theory, it is shown that the skewness of sea surface winds, damped by nonlinear surface drag, are consistent with the MEP principle. Then it is pointed out that the observed wavenumber spectrum of long planetary waves in the midlatitudes can be roughly explained by maximizing the meridional eddy heat flux (and related entropy production) of unstable baroclinic Eady waves. Finally observational evidence is presented that the meridional eddy heat flux is increased by non-Gaussian variability in meridional wind and temperatures anomalies.