Coriolis effects in homogeneous and inhomogeneous katabatic flows

Katabatic flows along a planar slope in a viscous stably-stratified fluid are investigated analytically and numerically, with an emphasis on flow features arising from the action of the Coriolis force. Two idealized flow types are considered: turbulent flow along a uniformly cooled slope, and two-dimensional laminar flow induced by a cold strip of finite width running down the slope. In the case of turbulent flow along a uniformly cooled slope, the downslope velocity exhibits a boundary-layer structure, but the cross-slope velocity and buoyancy fields spread inexorably upward. This behaviour is qualitatively similar to that found in laminar flows along a uniformly cooled slope. In contrast, in the two-dimensional strip flow, a steady state is reached, in which the cross-slope wind and buoyancy fields vanish far above the slope, but the downslope and slope-normal velocity fields do not vanish. These latter two flow components comprise two purely horizontal along-isentrope counter-flowing currents: an upslope current entering the top of the boundary layer on one side of the strip, and a downslope current flowing out of the boundary layer into the environment on the other side of the strip. The slope-normal vorticity associated with these currents originates in the stretching of planetary vorticity in a broad zone of convergent flow over the cold strip. Copyright  2008 Royal Meteorological Society