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