Thermodynamic efficiency of atmospheric motion governed by the Lorenz system.The Lorenz system was derived on the basis of a model of convective atmospheric motions and may serve as a paradigmatic model for considering a complex climate system.  In this study we formulated the thermodynamic efficiency of convective atmospheric motions governed by the Lorenz system by treating it as a nonequilibrium thermodynamic system.  Using these calculations, the thermodynamic efficiency was formulated for stationary and chaotic dynamics.  The numerical results show that for both stationary and chaotic dynamics, the efficiency tends to increase as the atmospheric motion is driven out of thermodynamic equilibrium when the Rayleigh number increases.  The analysis of the entropy generation rate was also performed for elucidating the difference between the thermodynamic efficiency of conventional heat engines and the present atmospheric heat engine. 
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