Wave Drag Effects in a Mesoscale Model with a Higher-Order Closure Turbulence Scheme

An incompressible, mesoscale model is used to estimate wave drag (WD) profiles over inhomogeneous 2D terrain. The goal is twofold: to evaluate the WD based on the model's fields and to analyze the atmospheric boundary layer (ABL) response to wave breaking. The model employs a simplified higher-order closure scheme for turbulent fluxes. A sponge layer mimics a radiative upper boundary condition (BC). Due to the no-slip lower BC for dissipative flows, the Eliassen-Palm theorem is not fulfilled and WD is generally not constant with height. Within the lower troposphere, the model's mean WD values compare to those from theory and other simulations. Above the ABL, where no physical processes dissipate waves, WD attenuates with height to roughly one-third of its theoretical value. This is mainly due to numerical dissipation of the used first-order advection scheme. However, the acceleration identified with the wave pattern reduction is small compared to governing accelerations. Two simulation sets are presented: one is a linear and another is a nonlinear airflow. The latter exhibits wave overturning and alters the ABL from above. The ABL becomes horizontally inhomogeneous over a distance equal to several times the characteristic width of the ridge.