Parameterization of the Planetary Boundary layer for Use in General Circulation Models 1

Abstract

Abstract Results of numerical integrations are presented for a neutrally stratified planetary boundary layer containing a passive scalar, and for three unstable cases with upward heat flux. The air is assumed unsaturated. A total of either 16,000 or 32,000 grid points was used in a three-dimensional region with length and width several times the height of the boundary layer. A key result is the irrelevance of the neutral height scale, u/f, and its replacement by the height zi of the inversion base which confines the convective mixing when &minuszi/L is as small as 1.5 (L is the Monin-Obukhoy length). Shapes of the eddies are examined for &minuszi/L=0, 1.5, 4.5 and 45; and only for the two slightly unstable cases were the vertical velocity eddies distinctly elongated as in Ekman-layer theories. At large instabilities it is shown how the friction velocity u/ loses its influence upon the turbulence intensifies and a convective velocity wale becomes important. Vertical profiles of mean wind, potential tempe...