Scale dependence of entrainment-mixing processes and microphysical properties: facts from observations, insights from theory, and implications for related parameterizations

Abstract:

Turbulent entrainment-mixing processes, cloud microphysics and their interactions need to be parameterized in models of widely different scales, ranging from large-eddy simulation models to cloud-resolving models to regional and global climate models. This necessity ---- similar need for climate models with different resolutions ---- poses a great challenge because all of these processes tend to be scale-dependent in ambient clouds, a topic poorly understood and studied itself. This work aims to understand the scale-dependence of these processes/properties from both observational and theoretical perspectives, and to explore the potentials for developing scale-dependent parameterizations. We will examine the dependence of entrainment-mixing mechanisms and microphysical properties on the averaging scale in clouds using data collected during the RACORO and other field campaigns. A new measure is introduced to quantify the entrainment-mixing processes. The relationships between the entrainment-mixing measure and microphysical properties and their scale dependence will be examined as well. We will also seek to connect the observational phenomenology to the systems theory on droplet size distributions, to explore ways to parameterize the scale-dependence for models of various resolutions, and to test with atmospheric models.