Nonlinear Processes in Geophysics www.nonlin-processes-geophys.net 1023-5809 1607-7946 15 1 2008 10.5194/npg-15-33-2008 http://www.nonlin-processes-geophys.net/15/33/2008/ http://www.nonlin-processes-geophys.net/15/33/2008/npg-15-33-2008.html http://www.nonlin-processes-geophys.net/15/33/2008/npg-15-33-2008.pdf 33 52 2008-01-31 Channelling of high-latitude boundary-layer flow N. Nawri nawri@meteo.mcgill.ca R. E. Stewart Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Canada Due to the stability of the boundary-layer stratification, high-latitude winds over complex terrain are strongly affected by blocking and channelling effects. Consequently, at many low-lying communities in the Canadian Archipelago, including Cape Dorset and Iqaluit considered in this study, surface winds for the most part are from two diametrically opposed directions, following the orientation of the elevated terrain. Shifts between the two prevailing wind directions can be sudden and are associated with geostrophic wind directions within a well defined narrow range. To quantitatively investigate the role of large-scale pressure gradients and the quasi-geostrophic overlying flow, an idealised dynamical system for the evolution of channelled surface winds is derived from the basic equations of motion, in which stability of stationary along-channel wind directions is described as a function of the geostrophic wind. In comparison with long-term horizontal wind statistics at the two locations it is shown that the climatologically prevailing wind directions can be identified as stationary states of the idealised wind model, and that shifts between prevailing wind directions can be represented as stability transitions between these stationary states. 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