Atmospheric stirring measured by precipitation

Abstract

Since on the average the water-content of the atmosphere is not increasing, the water which descends as precipitation must have been stirred up into the atmosphere. So we can compute the eddy-diffusivity from a knowledge of the mean precipitation and the mean vertical gradient of mass of water per mass of atmosphere. Eddy-diffusivity is a statistical measure of the effect of circulatory motions which we cannot, or do not wish to, consider in detail. Since the mean values in this paper are taken over the whole globe, it follows (unfortunately) that even the largest circulatory motions between the pole and the equator are not considered in detail, and that their effect is included with the effect of the rising currents in cyclone or anti-cyclones, with cumulus-eddies, and with the smaller eddies due to dynamical instability, in producing the coefficients of eddy-diffusivity at which we shall arrive.