Several PBL parameterization lessons arrived at running an NWP model

Several planetary boundary layer and turbulence transport parameterization advancements are reported upon, with the majority of them discovered by looking for a solution to a problem noticed in the course of running an operational NWP model. A surprising degree of sensitivity was repeatedly discovered to solutions found, with the refinements resulting in substantial improvements in the realism of forecasting a variety of actual atmospheric events. These improvements came from a reformulation of the Mellor-Yamada level 2 parameterization of surface fluxes via a change in the associated length scale; from a number of refinements in the specification of the Mellor-Yamada level 2.5 master length scale; and from the discovery of the reason for and improved handling of its realizability problem. Examples of the impact are shown. A refinement is summarized of the explicit molecular sublayer parameterization of Janjic, used over water as a constant-gradient approximation of the Liu, Katsaros and Businger relations. The refinement is arrived at by application of a momentum flux data summary and a suggestion by Brutsaert.