Some Problems on Edding Diffusion

[摘要] If we assume that the mixing lengths of x, y-components (x-axis coincides with the direction of gradient wind) are not equal, and write the components of eddy velocity in the form following Prandtl's treatment, we can readily derive the coefficient of eddy viscosity along x-and y-direction in the form:As the value of U and V, we adopted Ekman's spiral which has been observed by Mr. Fedor Schwandke at Hall/Leipzig and Hannover during the year from 1930 to 1933, and determined the value of ∂U/∂z, ∂V/∂z at each height by graphical method.First we adopted Taylor's equipartition theory of edding energy, and discussed the value l1, l2 at each height. Thus we found that in the lower atmosphere the relation l2>l1 holds, which, with the approach to the height of gradient wind, tends to the relation l2=l1.Next we rely on F. J. Scrase's observation. Assuming the relation l1=l2, we discussed the distribution of eddy velocity at each height. The value u'/v' thus obtaind gives a maximum value at a height of 100m and decreases with height.Assuming rather a general case in which neither the condition v'2=u'2 nor l1=l2 exists, wealso obtaind approximately the relation l2_??_l1, in the lower atmosphere. On account of the above discussion, we may conclude that the coefficient of eddy viscosity has a large value in the perpendicular direction to the general flow.Adopting the coefficient of eddy viscosity k1, k2 we solved the equation of eddy motion. As the relation between surface wind and gradient wind, we have the following form.which, of course, in case of k1=k2 reduces to Taylor's relation.

[学科分类] 大气科学