Large Eddy Simulations (LES)

Within this activity we pursue a twofold goal. First, to gain a detailed understanding of small-scale processes, and second, to use the LES as a surrogate reality. We then derive the resolution requirements and best settings for kilometer-scale simulations from these high-resolution simulations. A version of the COSMO-CLM model employing a Smagorinsky-Lilly scheme for the parametrization of turbulence has been developed, which allows to decrease the grid spacing to O(10 m).

Convection over mountainous terrain poses a challenging task. Diurnal slope and valley winds are an essential component of the fair-weather mountain atmosphere. They strongly influence the weather and climate in mountain valleys and together with turbulent processes they control the land surface-atmosphere exchanges in mountainous regions and thus influence the development of clouds and deep convection. More-over, inhomogeneities in the soil-moisture distribution affect the time and location of the triggering of clouds and precipitation. The focus of this activity is on the basic physical mechanisms governing the evolution of the developing convection and on its numerical simulation.

Panosetti D., S. Böing, L. Schlemmer and J. Schmidli, 2016: Idealized large-eddy and convection-resolving simulations of moist convection over mountainous terrain. J. Atmos. Sci., 73, 4021–4041, external pagehttps://doi.org/10.1175/JAS-D-15-0341.1

Schlemmer L., P. Bechtold, I. Sandu and M. Ahlgrimm, 2017: Uncertainties related to the representation of momentum transport in shallow convection. J. Adv. Model. Earth Syst., 9, external pagehttps://doi.org/10.1002/2017MS000915.