A Note on the Pure Katabatic Wind Maximum over Gentle Slopes

The wind maximum of pure katabatic winds over moderate slopes, the inclination varying between 3 and 6A degrees, is studied using large-eddy simulation (LES) and further discussed in the light of the classical Prandtl model. The LES results show that both the maximum katabatic wind speed and its height decrease with increasing slope angle, and vice versa. However, in the Prandtl analytical, i.e. linear classical, solution, only the wind maximum height is affected by the slope angle, not the maximum wind speed. For the given range of slope inclinations, a linear relation between the height and the magnitude of the wind maximum is found in our simulations, which is supported by a limited dataset obtained by other researchers; these results are further discussed. The inability of the analytical Prandtl solution to give the maximum wind-speed dependency on the slope angle is associated with the assumed constancy of (1) the background vertical potential temperature gradient I, (2) the eddy diffusivity and (3) the Prandtl number.