P83 Nested realistic daily WRF-LES simulations using eddy-seeded lateral boundary conditions

Gaudet, Brian J., Aijun Deng, David R. Stauffer, Nelson L. Seaman, and Astrid Suarez, Penn State University

For grid spacing on scales smaller than those of the energy-containing turbulent eddies in the planetary boundary layer (PBL), it becomes appropriate to model turbulent structure with the large eddy simulation (LES) method. WRF has the capability of being run in LES mode as a nest within a coarser domain that uses Reynolds-averaged PBL parameterizations, while at the same time containing realistic topography and heterogeneous atmospheric features. Time is required for realistic eddy structures to develop in an LES after initialization. These populate the LES domain when periodic lateral boundary conditions (LBCs) are used. However, for realistic topography, nonperiodic LBCs are needed, and if there is a mean horizontal flow, eddy-deficient regions will tend to develop near the inflow boundaries.

Here we present examples of the WRF-LES model (Δx = 111 m) recently running as nests within one of our high-resolution WRF configurations that run on a daily basis over central PA. We show how the use of an eddy seeding relaxation method, previously applied to single-domain idealized LES, can also produce more realistic eddy structures in a realistically heterogeneous LES nest. Different methods of treating the LBCs on the innermost domain will be contrasted and evaluated.