Synthetic aperture radar and high-resolution MM5 simulations of barrier jets in coastal Alaska

The mesoscale atmospheric flow near coastlines with prominent terrain lias a tremendous impact on those who live and work in the coastal environment. One of the most common of these terrain-induced flows, the barrier jet, creates especially dangerous weather conditions, particularly in southeast Alaska and the Pacific Northwest. The resulting severe winds pose a threat to life, property and economic activities. They play a major role in safety at sea for the fishery and oil industries. Barrier jets occur when stable onshore flow interacts with a mountain barrier. In classical barrier jet theory, the barrier normal flow is blocked when the Froude number is much less than 1. In these situations, the onshore flow is too stable to rise over the barrier. The dynamic response is for the ascending air to cool and generate a hydrostatic positive pressure perturbation which forces a turning of the wind to the left along the barrier in the Northern Hemisphere. The Gulf of Alaska is uniquely suited to studying barrier jets of both the classical and hybrid types. This is because of the frequency of onshore flow events associated with landfalling synoptic cyclones, the mountain ranges with complex dimensional terrain (including gaps) that occur along large sections of the coast, and the orientation of the coast line (particularly along the SE coast of the Gulf). In addition, the fact that much of the Gulf lies at high latitudes ensures excellent coverage from polar orbiting satellites such as the scatterometer aboard QuikSCAT and the synthetic aperture radars aboard the ENVISAT and RADARSAT-1 satellites.