Two-dimensional katabatic flows along a planar slope

Katabatic flows in nature may be influenced by a variety of surface inhomogeneities including irregular snow/ice/soil cover, topographic shading, spatial variability of soil moisture, land use and terrain complexities. One of the simplest possible frameworks for considering some of these influences is to look at the impact of surface thermal forcings that are irregular in preferred directions (e.g., purely along-slope or purely cross-slope). In this study we consider the idealized problem of katabatic flows of a stably-stratified fluid induced by surface cooling that is confined to a strip of finite width in the along-slope direction, but of infinite extent in the cross-slope direction. Coriolis effects are neglected. The governing parameters for this flow are the environmental buoyancy frequency, mixing coefficients, surface buoyancy, slope angle and strip width. The non-dimensional problem is thus governed by four degrees of freedom. Preliminary direct numerical simulation experiments suggest the existence of a wide range of flow structures and behaviors, including gravity currents, internal gravity waves, classical katabatic boundary layers, rotors (both up- and down-slope from the strip), and jet-like flows entering and leaving the vicinity of the strip horizontally along isentropes. These latter structures are reminiscent of the horizontal intrusions observed in lakes in which cold river water surges down the slope until it encounters its level of neutral buoyancy.