Estimating the convective velocity scale for diffusion applications

A simple mixed layer model is used to derive the following expressions for the maximum (daily) convective velocity scale. w _*m = AQ _m ^1/2; w _*m = Bz _im The variables A and B are shown to vary within narrow limits thus allowing them to be treated as constants. This is very useful for routine computation of w _*m , an important variable for dispersion under unstable conditions, from estimates of either the kinematic surface heat flux Q _m (m^-1) or the maximum mixed layer height z _im .Analysis of observations made during the Minnesota boundary layer experiment shows that there is ample justification for assigning typical values to A and B in estimating w _*m.