Gap Winds in a Fjord. Part I: Observations and Numerical Simulation

Gap winds in Howe Sound, British Columbia, are described and placed in context by reviewing studies of similar phenomena in other locations. An observational program consisting of a surface mesonetwork and vertical soundings shows that gap winds vary considerably along and across the channel, as well as vertically. Wind strength generally increases down channel, and strongest winds are found below 1000-m depth. Results from application of a 3D mesoscale numerical model to a gap wind case compare reasonably well with observations. Model output reveals more details of horizontal and especially vertical flow structure than is possible from observations. Model vertical cross sections and Froude number output indicate similarity with hydraulic flow. This is further substantiated by a force-balance analysis of model output.