Vertical Velocity in Shallow Convection for Different Plume Types

Abstract:

This study investigates the bulk budgets of the vertical velocity and its parameterization in convective cores, convective updrafts, and clouds by using large-eddy simulation (LES) of four shallow convection cases in the Global Energy and Water Cycle Experiment (GEWEX) Cloud System Study (GCSS) programs. The relative magnitudes of the dominant momentum budget terms for the three types of plumes are presented. For all shallow cumulus except stratocumulus, the buoyancy force and the subplume transport in the core plume are the momentum source that offset the pressure gradient force. In the cloud updraft and cloud plumes, the buoyancy source is dominant in the lower and middle parts of the clouds, while the subgrid transport is a dominant source in the upper part, and the entrainment term is also a momentum source. For the stratocumulus, the subplume transport is a sink almost in the whole convective layer. For all types of plumes, the Simpson and Wiggert (1969) equation is found to be good paramaterization of the mean plume vertical velocity when appropriate scaling coefficients to buoyancy and entrainment terms are used. Optimal forms of the Simpson and Wiggert equation are given for convective cores, convective updrafts, and convective clouds. Results are compared with other studies published in the literature.