Dynamical Modeling of Flow in Cumulus-Filled Boundary Layers

Abstract

A primitive equation planetary boundary layer (PBL) model is constructed and applied to simulate the downwind evolution of coupled dynamic, thermodynamic and cloud properties in the PBL over warmer mean. A multilayered approach is adopted to model the inversion-capped convective PBL filled with shallow cumuli, stratocumulus clouds, or cloud-free air. Vertically varying turbulent and convective cloud fluxes are constructed from recently published parameterization schemes. This model is designed to simulate some influences of cloud, vertical mixing, and horizontal advection on surface winds over much of the world's oceans. An initial application is the local simulation of trade wind flow using a one-dimensional version of the model. Modeled vertical momentum flux and wind in the cumulus-filled baroclinic PBL agree well with observations, confirming the validity of the momentum parameterization scheme. Applications to two-dimensional simulation of a moderate cold surge over a warm ocean show the enhancement of mixing processes by shallow moist convection. The resulting changes in the PBL mass field show a significant effect on the PBL horizontal pressure gradient forces and wind fields during air mass transformation.