Far-field vortex structures in mountain wakes

Abstract

Laboratory experiments on scaled mountain wakes have provided the first demonstration that indicates the existence of two distinct mechanisms for the formation of the long-lived vortex structures that have been frequently observed in satellite imagery. In a series of laboratory experiments the well-known von Karman vortex shedding mechanism has been observed at low values of Froude number (corresponding to low speed flow and strong stratification). At high Froude numbers the initial highly turbulent wake evolves into a vortex pattern similar to the far-wake dipole eddies previously observed in laboratory studies of submerged stratified wakes. In satellite imagery vortex structures have been observed to persist for hundreds of kilometers. In the present laboratory experiments far-wake dipole eddies were observed to persist for at least 200 diameters downstream, which corresponds to ~4,000 km when scaled to actual mountains. When generated at multiple sites along a continental mountain chain, these eddy structures could play a significant role in the development and variability of multi-scale weather and climate patterns.