A new boundary layer mixing scheme. Part I: Scheme description and single-column model tests

A new boundary layer turbulent mixing scheme has been developed for use in the UKMO weather forecasting and climate prediction models. This includes a representation of nonlocal mixing (driven by both surface fluxes and cloud -top processes) in unstable layers, either coupled to or decoupled from the surface, and an explicit entrainment parameterization. The scheme is formu lated in moist conserved variables so that it can treat both dry and cloudy layers. Details of the scheme and examples of its performance in single-co lumn model tests are presented.