Three-Dimensional Simulation of Turbulent Processes in an Undisturbed Trade Wind Boundary Layer

The numerical model used by Deardorff (1972) for studying the clear air boundary layer under neutral or unstable conditions has been extended to include most of the physical processes occurring in a moist boundary layer in the absence of precipitation. It now contains a water cycle with cloud formation and a revised treatment of the subgrid-scale turbulence which incorporates effects of thermal stratification; it takes Into account infrared radiative cooling in clear and cloudy conditions and the influence of large-scale vertical motions and horizontal gradients. Section 2 includes a description of the model with emphasis on its new features. Section 3 presents some results obtained in a simulation of the trade wind boundary layer with detailed treatment of cloud dynamics in the absence of precipitation. The simulation shows how the turbulent characteristics evolve with time toward a statistically steady state, with an example being given of the turbulent field in the presence of clouds. The relative importance of the various physical processes in the evolution of the mean field of variables is indicated.