A Height-Dependent Model of Eddy Viscosity in the Planetary Boundary Layer

Abstract

A height-dependent model of the vertical eddy diffusivity for momentum, K(Z), has been formulated for purposes of studying numerically the momentum (and heat) transfer arising from turbulent motions within the planetary boundary layer (PBL). The model possesses those features believed to be characteristic of the PBL: 1) an approximate linear increase in K through the surface boundary layer, 2) a local maximum value of K in the lower portion of the Ekman layer, 3) an exponential decrease in the profile above the level of maximum K, and 4) a K(Z) function that is continuously differentiable. Specifically the model is given aswhere Z represents height, ZT the top of the PBL and the scaling factor, and a, b and c are arbitrarily chosen parameters that specify a unique K profile. The applicability of the model to atmospheric data is shown by fitting curves to the K distributions derived by Pandolfo's study using BOMEX data.