Use of a Modified Richardson Number for Parameterizing the Effect of Shallow Convection

Abstract

 In the framework of a if-exchange parameterization for PBL turbulent fluxes we propose a simple way to include the effects of shallow convective clouds. The method is dimensionally consistent with cloud buoyancy production, is cheap and avoids the introduction of additional arbitrary parameters by simply extending the dependency of the exchange coefficient on the Richardson number from the dry to the moist case.
 In the case of the french large scale operational model it is very efficient in suppressing the defects associated with the PBL collapse that is usually observed when one uses only “dry” K-coefficients.