Towards 1-Kilometer Resolution Weather and Climate Simulations (2013-2015)
C2SM aims to refine climate and weather model resolution in order to better reproduce small-scale phenomena and is involved in the development of a 1km operational version of the COSMO model through an on-going project led by MeteoSwiss.
Weather and climate simulation at O(1km) resolution in the turbulence "greyzone" requires a careful inspection of the underlying model assumptions. New and improved parameterizations which are better adapted to these scales are needed.
The “Turbisim” project is part of the development of 1-kilometer resolution weather forecasts at MeteoSwiss (COSMO-1). C2SM-community members Steven Böing and Jürg Schmidli are part of the project. At this resolution, thunderstorms are explicitly resolved, while shallow clouds and turbulence are not. Current kilometer-scale simulations show significant biases, typically with too late triggering of deep convection and too strong precipitation. We work towards a unified representation of shallow clouds and turbulence and a better representation of resolved deep convection.
The project team is currently setting up Large Eddy Simulations of convection over topography with a horizontal resolution of 100 meters. These simulations will serve as a reference to test new developments on the representation of turbulence and subgrid-scale clouds in COSMO. We will look at the formulation of horizontal and vertical mixing and the role of unresolved variability in vertical velocity, temperature and moisture. Topography adds more complexity, since it creates small scale circulations. The interaction of these mountain flows with convection is a challenge for current weather models.