The vertical cloud mass flux is a key ingredient in parameterizations of convection, including dry and shallow cumulus. The exact behavior is strongly dependent on the precise definition of the cloud, with a larger mass flux for the cloud core and a smaller one for a simple liquid water threshold, and yet smaller with attempts to include the subsiding shell. In recent DNS studies, we observe a Turbulence-Non-Turbulence Interface (TNTI) with relatively little lateral mixing across this interface.
Such an interface appears to exist as well in high resolution (5m grid spacing) LES of shallow convection, albeit distorted by shear and other sources of turbulence. Furthermore, the TNTI defined cloud is much longer lasting than the liquid water defined cloud, thus capturing more of the cloud decay process. In this study, we will evaluate the mass flux, entrainment, and detrainment, as well as the cloud life time and cloud size distribution as a function of cloud definition and threshold. We explore the strength of these parameters as a function of microscopic quantities like local enstrophy as well as the macroscopic local turbulence kinetic energy and the global shear levels. Finally, we can use these definitions to more easily harmonize the relation between the subcloud- and cloudy convection.
Thijs Heus is associate professor of physics at Cleveland State University. His research interests include the physics of climate, focusing on clouds. Clouds are the biggest unknown in the climate system, because they are involved in many feed back cycles. By doing large computer simulations, he aims to understand how clouds grow, transport heat and moisture, start to rain, and organize in clusters (or not).