Simulating a Cold-Air Outbreak with SHOC (Simplified Higher-Order Closure)

The Grey Zone Project aims to systematically explore convective transport and cloud processes in weather and climate models at various resolutions, ranging from high resolution turbulent resolving scales all the way to coarse resolutions that require full parameterized descriptions of these processes. The first Grey Zone intercomparison case is based on observations of a cold air outbreak during the CONSTRAIN field campaign. The purpose of the intercomparison is two-fold: First, through systematically varying the horizontal resolution, the intercomparison will aim to assess the relative contributions of the resolved and the subgrid-scale (SGS) cloud and convective processes in the Grey Zone for the present CONSTRAIN case. Second, the intercomparison is interesting in its own right as it is the first time that a comprehensive mid-latitude cold-air outbreak case has been organized. We will participate by using a version of a cloud-resolving model, SAM (System for Atmospheric Modeling), that includes SHOC (Simplified Higher-Order Closure, Bogenschutz and Krueger 2013) which combines several existing components: A prognostic SGS turbulence kinetic energy (TKE) equation, an assumed double-Gaussian PDF following Golaz et al. (2002), the diagnostic second-moment closure of Redelsperger and Sommeria (1986), the diagnostic closure for <w'w'w' > by Canuto et al. (2001), and a turbulence length scale related to the SGS TKE (Teixeira and Cheinet 2004) and to eddy length scales.