Boundary Layer Effect on the Frontal Interaction with Mountain,

A hydrostatic, primitive equation model with frontogenetical deformation forcing is used to simulate the passage of cold fronts over a two dimensional ridge. The model includes a K-theory boundary layer PBL parameterization with implicitly defined diffusion coefficients. Relative to the inviscid results, the PBL simulations produced reduced frontolysis on the upwind slope and reduced frontogenesis on the lee slope, resulting in significantly smaller frontogenetic variations over the mountain. This is caused by convergence forcing in the well-mixed layer offsetting the overall frontolytical forcing on the upwind slope, and greatly reduced lee side convergence forcing due to the PBL. In contrast to the inviscid results, the final downstream front is weaker in the mountain simulations than in the flat-topography control case when PBL effects are included.