Large Eddy Simulations of Fair-Weather Cumulus Case at SGP Site
Zhu, P. and Albrecht, B.A., University of Miami
Twelfth Atmospheric Radiation Measurement (ARM) Science Team Meeting
A fair-weather cumulus (FWC) case observed on July 6, 1997 at the ARM SGP site is simulated using RAMS model. In this study, we performed a series of numerical experiments to study the basic physics underlying the FWC and the evolution of these clouds in response to the change of external forcings and conditions. The simulations indicate that the evolution of shallow cumuli is very sensitive to the initial vertical structure of moisture and the variation of the entrainment moisture fluxes. Based on the penetration theory, we are able to develop a cloud initiation parameterization using the variables that may be provided by large-scale models. It is found that the surface sensible heat flux can significantly affect the cloud initiation time and cloud base height, but has limited influence on other important cloud properties such as cloud cover fraction and liquid water path (LWP). In contrast, the surface latent heat flux may have strong impact on these two cloud properties. The two other factors that may significantly affect the cloud development are the moisture difference across the top of the CBL and the stratification above the CBL. Horizontal winds, however, have little influence on changing cloud properties even though they have a strong effect on cloud organizations. By coupling the atmospheric model with a soil model, we also studied the impact of cumuli on the turbulent transport within the CBL. We verified the change of various turbulent fluxes due to the existence of cumuli.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
