Similarity statistics from a direct numerical simulation of the neutrally stratified planetary boundary layer

The turbulent flow in the unstratified Ekman layer over a smooth surface fo r the case of no horizontal rotation has been simulated. All relevant scale s of motion are resolved so that no subgrid-scale parameterization is neede d. The Reynolds number Re, while much smaller than those found in the atmos phere, is large enough that the flow exhibits a distinct logarithmic surfac e layer and yields shear-stress statistics that, to a good approximation, s atisfy Reynolds number similarity. Agreement with shear-stress profiles fro m large eddy simulations is good, especially when latitude and geostrophic wind direction are taken into account. Results are used to estimate the rat io of the boundary layer depth to the Ekman scale u(*)/f and the similarity constants needed to determine the geostrophic drag coefficient u(*)/G and surface-stress angle alpha(0) in the Re --> infinity limit characteristic o f the neutral planetary boundary layer.