On integral measures of the neutral barotropic planetary boundary layer

Two types of neutral planetary boundary layer (PBL) are distinguished: truly neutral - developed against a neutrally stratified free flow, and conventionally neutral - developed against a background stable stratification. Atmospheric PBLs treated as neutral are almost always conventionally neutral. Theoretical reasoning and results from large-eddy simulation (LES) show that A and B coefficients of the Rossby-number similarity theory are not constants. The same is true for the coefficient C-h in the Rossby-Montgomery formula for the neutral boundary-layer depth h = C(h)u*/\f\, where u(*) is the friction velocity. Contrary to classical ideas, A, B and C-h depend on the ratio mu(N) equivalent to N/\f\ of the free-flow Brunt-V*auml;isal a frequency N to the absolute value of the Coriolis parameter |f|. This new development can explain why atmospheric and LES estimates of A, B and C-h appear inconsistent. It results from neglecting the fact that atmospheric data for mu(N) similar to 10(2) were compared with LES data for mu(N) = 0, violating an obvious requirement of similarity with respect to mu(N).