Size distribution of dust devils in the atmosphere

On the basis of the principle of maximum informational entropy, the equilibrium exponential size (visible diameter) distribution of dust devils in the atmosphere has been introduced. Two independent sets of statistical data on dust devils observed respectively in Arizona and south California are in good agreement with the reference exponential distribution, although the average diameters of the vortices in these two data sets differed by a factor of 5 from each other. The estimates obtained in the paper have indicated that the average diameter of a dust-devil vortex and the doubled value of the Monin-Oboukhov scale are close to each other, a result which was previously observed during dust devils in Australia. A physical explanation is proposed for the closeness of statistics observed for dust devils to the equilibrium exponential distribution. This explanation is based on the property of additivity for the Kelvin circulation of wind velocity in vortices and on a weak dependence of the maximum tangential wind velocity on the size of a vortex. On a heuristic level, it is considered whether the equilibrium exponential distribution is applicable to dust devils observed in the Martian atmosphere.