Gap Winds in the Strait of Juan de Fuca

Abstract

Gap winds can be defined as a flow of air in a sea level channel which accelerates under the influence of a pressure gradient parallel to the axis of the channel. In February 1980 two distinct cases of gap winds were observed in the Strait of Juan de Fuca between western Washington State and British Columbia during a study that measured spatial variation of low-level marine winds and other parameters from the NOAA P-3 research aircraft and a dense network of surface stations which included eight meteorological buoys. These two cases were a high-pressure region over central British Columbia and a low-pressure system propagating northward, seaward of the Washington coast. Both cases produced strong easterly winds of 13?15 m s?1 at the western end of the Strait of Juan de Fuea. The high-pressure region provided a drainage air mass from the interior of British Columbia which flowed through the Straits of Georgia and Juan de Fuca and eventually into the Pacific Ocean. This air mass remained nearly homogeneous and was capped by a well-defined inversion. For the offshore low-pressure center, the lower atmosphere was stably stratified throughout the region, and weak winds were observed at the eastern end of the Strait of Juan de Fuca with strong winds at the western end. Although the features of the flow fields were complex, major characteristics of the wind fields can be accounted for by the combined effect of topography and the synoptic pressure field. Local winds were in approximate ageostrophic equilibrium between the inertia term and the imposed sea level pressure gradient.