The onset of shallow cumulus clouds at the top of a convective boundary layer (CBL) has significant impact in the subsequent development of the boundary layer. Besides their effects on the radiative fluxes reaching the surface, cloud fluxes can be significant components of the boundary layer budgets of enthalpy, water vapor, and other species. Moreover, clouds modify the moisture and temperature profiles of the atmospheric layer above the CBL, therefore affecting the growth rate of the CBL and the properties of the air entraining at its top.

We investigate the interactions between the boundary layer and shallow clouds using the 3-D MM5 mesoscale modeling system, with a 1.5 Order TKE turbulence scheme and the Penn State Shallow Convection parameterization developed by Deng et al. The latter can be considered an extension of the Kain-Fritsch deep convective parameterization, for the cases of non-precipitating clouds.

We will present results for a summertime case study in July 1997 focusing in the Central Plains region. We will describe the effects of the shallow convection parameterization on the evolution of the CBL and the cloud-layer environment in a 12-hour simulation verified using data from the Southern Great Plains ARM-CART database. Results are evaluated in terms of how well the model captures the observed mesoscale gradients of clear air, shallow convection and deep convection. Sensitivity to the soil moisture distribution and the inclusion of the Penn State shallow convection parameterization are demonstrated in this complex convective environment.