Physical Aspects of Rapid Cyclogenesis in the Gulf of Alaska

The Gulf of Alaska is often the site of rapid development of large-scale cyclonic activity which can have profound effects on the long-wave pattern over North America in a matter of 24 to 48 hours. During much of the year such cyclogenesis takes place in the presence of a large heat source associated with rapid modification of cold Arctic air masses moving from Alaska out over the warmer sea surface of the Gulf. In order to get some insight into the mechanism of cyclogenesis under these special conditions a case of intense development occurring early in February 1950 has been studied, mainly in terms of the vorticity equation. The effects of barotropic redistribution of vorticity seem to account for much of the development. However, it is found that there exist pronounced fields of divergence and vertical motion, which particularly at the time of most rapid development reflect the influence of heat sources on the circulation.