The Dynamics of Mountain-Wave Induced Rotors

The development of rotor flow in two-dimensional mountain waves is investigated through a series of high-resolution simulations with the COAMPS model. The generation of rotors and associated regions of low-level reversed flow is shown to be closely linked to the viscous production of horizontal vorticity in the planetary boundary layer. Differences in the morphology of free-slip flows and no-slip flows in the limit of vanishing surface friction are discussed. Of course even with the inclusion of surface friction, not all large-amplitude mountain waves produce rotors. Those factors, besides surface friction, that favor the development of rotors are identified and discussed.