A Higher-order Turbulence Closure Incorporated with Prognostic Planetary Boundary-Layer Height for Use in Climate Models

Realistic simulations of boundary layer clouds in climate models are difficult to achieve without vertical grid spacing well below 100 m, especially for stratocumulus-topped boundary layer. The need for fine vertical grid spacing presents a significant impediment to global variable-resolution and fine-resolution simulations, including the Multiscale Modeling Framework. In MMF, a 2-D cloud-system resolving model is embedded into each grid cell of a global climate model in place of traditional cloud parameterizations. One potential solution to this impediment is to predict the planetary boundary-layer (PBL) height to resolve the discontinuities at the boundary-layer top. In this study, we examine simulations with a prognostic PBL height approach for three well-studied cases based on observations from the second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) experiment, the Atlantic Stratocumulus Transition Experiment (ASTEX), and the Atlantic Trade Cumulus Experiment (ATEX). The preliminary results show the strength of the cloud top entrainment, the inversion of the liquid water potential temperature and the total water, and the turbulence transport are more realistically represented when the PBL height is predicted. The additional benefits of this approach are that the time-step for the turbulence closure scheme can be larger and the vertical grid-spacing can be larger.