3.5    Eddy Seeding for Improved WRF-LES Simulations Using       Realistic Lateral Boundary Conditions

Gaudet, Brian, The Pennsylvania State University, and Aijun Deng, David Stauffer, and Nelson Seaman, The Pennsylvania State University

The WRF-ARW model is capable of physically representing the effects of turbulence in two distinct ways.  One way involves using parameterizations of the effects of turbulence on the mean state variables found within the boundary layer schemes of the physics module.  These are typically used when the horizontal grid spacing is significantly greater than the scale of the energy-containing eddies.  The other way is to run WRF-ARW in large eddy simulation (LES) mode, in which the energy-containing turbulent eddies are explicitly resolved, while the downscale cascade of turbulent eddies is accounted for by a subgrid parameterization.  WRF-LES can be used in a nested grid configuration, with a parent grid that uses a turbulence parameterization and realistic heterogeneous atmospheric and surface conditions, and nested grids using LES closure; however, non-periodic nested LES domains can suffer from deficient or unrealistic eddy structures near the lateral boundaries.

In this presentation we will show how nested WRF-LES non-periodic domains can be improved through the use of an Ôeddy seedingÕ method, using a library of stored eddy structures and appropriate scaling methods.  Comparisons will be shown with simulations using a version of the CM1 LES code that demonstrates the new method.  Future possible refinements of the method will also be discussed.