Origin of the Catalina Eddy

Abstract During late springs through early fall the normal regime of low-level westerly and northwesterly flow within the bight of southern California is occasionally interrupted by periods of southerly flow, elevated marine layers, and increased low-level cloudiness. This transition, often termed the Catalina Eddy, is limited to narrow zone of ∼100 km from the coastal mountains and brings cooler temperatures and improved air quality. This paper describes the initiation and evolution of Catalina Eddy events using both composite and case study approaches. It is found that this phenomenon is produced by the interaction between the synoptic-scale flow and the formidable topography of the region. As a result of synoptic-scale pressure falls along the central California coast and/or mesoscale lee troughing southeast of Point Conception, an alongshore pressure gradient with lower pressure to the north becomes established. The result of such a pressure gradient in a coastal zone with an adjacent topographic barr...