The 13th Symposium on Boundary Layers and Turbulence

3A.5RADIX LAYER DEPTH PARAMETERIZATION FOR WIND AND TEMPERATURE IN CONVECTIVE CONDITIONS

Edi Santoso, Univ. of British Columbia, Vancouver, Canada; and R. B. Stull

In the middle of the convective atmospheric boundary layer is often a deep layer of vertically-uniform wind speed (Mu), wind direction, and potential temperature (Tu). A "radix layer" (RxL) is identified as the whole region below this uniform layer (UL), where the winds are slower. The classical surface layer (SL), defined as the region where Monin-Obukhov similarity is valid, is a shallower subdomain of the radix layer. Radix is Latin for "root", named because the roots of convective thermals are in this layer.
The dimensionless similarity equation for wind (M) can be transformed into M / Mu = F(z/zR), where the profile function F that satisfies a smooth transition from the RxL to UL is empirically found to be F =( [(z / zR)D]A) * exp[A *(1 - (z / zR)D)] where A and D are constants. The same profile function F with different radix-layer depth and shape exponent is shown to describe the potential temperature profile (T - Tu) / (To - Tu) = 1 - F(z / zR), where To is the potential temperature near the surface, and T is the potential temperature at height z above ground level.
The depth of radix layer (zR) can be parameterized as a function of the surface friction velocity, u*, the Deardorff velocity, w*, and the mixed layer depth, zi, with relationship zR = C [(u* / w*)B]* zi, where C and B are constants. Results from the 1973 Minnesota data analysis show that the values of zR for wind are an order of magnitude higher than those for temperature. The values of A, B, C and D for both are not necessarily the same. Independent data from Boundary layer Experiment 1996 (BLX96) are used to validate these results.