PRESSURE DRAG OF OBSTACLES IN THE ATMOSPHERIC BOUNDARY-LAYER

Pressure drag of obstacles in the atmospheric boundary layer is computed with a mesoscale numerical model of the troposphere. The study shows among other points that there is a surface Rossby number similarity for form drag on smooth obstacles, that there may be wave drag due to inertial waves even for neutral or unstable stratification due to inertial waves, and that there is Reynolds number similarity for form drag only with respect to molecular viscosity and not with respect to turbulent viscosity of the air. The results suggest the separation of form drag into two parts: a viscous form drag due to turbulent viscosity of the air, and a turbulent form drag due to additional production of turbulence in the vicinity (mainly in the lee) of the obstacle. The distinction of different drag producing mechanisms will help in the task of parameterization. -from Author