The influence of a viscous boundary layer on trapped lee-waves a Viscous Boundary Layer

Abstract

The backward reflection of a stationary Gravity Wave (GW) propagating toward the ground is examined in the linear viscous case and for large Reynolds numbers (Re). In this case, the stationary GW presents a critical level at the ground because the mean wind is null there. When the mean flow Richardson number at the surface (J) is below 0.25, the GW reflection is total in the inviscid limit Re~infinite. The GW is a little absorbed, when Re is finite, and the reflection decreases when both the dissipation and J increase. When J>0.25, the GW is absorbed for all values of the Reynolds number, with a general tendency for the GW reflection to decrease when J increases. These results are applied to explain why the more unstable boundary layers favor the onset of mountain lee waves.