The realism of the model is evaluated by a direct comparison of the model predictions with the aircraft observations of the STBL. The first case study is based on the UKMRF flight 526 measurements collected over the North Sea on 22 July 1982; the second case study corresponds to the ASTEX flight A209 flown on 12-13 June 1992. The model is able to reproduce reasonably well most of the observed boundary layer parameters, including turbulent fluxes and variances of various fields, intensity and vertical distribution of the turbulent kinetic energy, upward and downward radiation fluxes, and the cloud drop spectra.I designed a new bulk microphysical parameterization using the explicit model as a benchmark for comparison. The liquid water is divided into two categories--non-precipitable cloud water and drizzle, similar to traditional Kessler-type parameterizations. The water content and drop concentration are predicted for each category. The source/sink terms such as autoconversion of cloud water into drizzle are deduced directly from the drop size spectra predicted by the explicit microphysical model. The predictions of the LES model using the new bulk microphysics are compared with the predictions using explicit microphysics for two cases: non-drizzling and heavy-drizzling STBL. The results show that the new bulk microphysical model satisfactorily reproduces many characteristics of the STBL as simulated by explicit microphysical model.A case of stratocumulus-to-cumulus transition triggered by the depletion of CCN is simulated. It is shown that the response of the STBL to the increase in drizzle due to CCN depletion is the reduction of its cloud fractional cover and change of the character of circulation toward the cumulus convection. The boundary layer after the Sc-to-Cu transition consists of two layers: the well-mixed cloud free surface layer driven by surface heat fluxes and shear, and the conditionally unstable upper layer capped by the inversion with embedded cumulus clouds connected to the moisture and CCN supply in the surface layer.A new LES dynamical framework coupled with an explicit microphysical module has been developed. It is verified against analytical solution (linear mountain wave test) and against predictions from the other LES models. The results of the tests of the microphysical module convincingly show that the drop spectrum resolution in our model is adequate to accurately predict the cloud microphysics parameters
