Climatology of Barrier Jets along the Alaskan Coast. Part I: Spatial and Temporal Distributions

Abstract

This paper investigates the temporal and spatial climatology of coastal barrier jets in the Gulf of Alaska. The jets are divided into two categories based upon the origin of the air involved: ?classic? barrier jets fed primarily by onshore flow and ?hybrid? jets fed primarily by gap flow from the continental interior. The analyses are compiled from five years (1998?2003) of synthetic aperture radar images from the Radarsat-1 satellite totaling 3000 images. Thermodynamic and kinematic data from the NCEP reanalysis is used in the interpretation of the results. The majority of coastal barrier jets occur during the cool season, with the coastline near Mount Fairweather and the Valdez?Cordova mountains experiencing the greatest number of barrier jets. Hybrid jets are even more strongly restricted to the cool season and are commonly found to the west of Cross Sound, Yakutat Bay, and Icy Bay. Some interannual variability in the total number of jets is observed. Coastal barrier jet formation is associated with onshore wind directions and maximum terrain heights exceeding 2 km within 100 km of the coast, features that support low-level flow blocking. Hybrid jet formation requires the additional condition of an abnormally large offshore-directed pressure gradient force. Half of the barrier and hybrid jets exhibit surface wind speeds in excess of 20 m s?1 (strong gale), although their widths are typically less than 100 km. The maximum speed of both types of jet tends to be 2?3 times that of the ambient synoptic flow. A small percentage of the jets detach from the coastline, with the typical detachment distance being 10 km.