The Catalina Eddy and Topographic Forcing over the Southern California Bight


Ten Catalina Eddy events are examined for the year 1996 with an expanded network of surface and upper-air data sets. Included are a network of three east-west oriented surface stations and a radar profiler on the south side of the Santa Ynez Mountains that are in the path of any lee side flow which has been proposed as initiating the Catalina Eddy. The hypothesis that lee-side effects of the Santa Ynez Mountains causes the formation of Catalina Eddy fails in all events when examined with the expanded observation network not utilized earlier. Several Eddy events have marine air thinning or constant height in the San Diego area during the formation stage which conflicts with the hypothesis that “cold air damming” causes marine layer deepening and the first appearance of the eddy in the San Diego area. A summer atmospheric marine layer transcritical expansion fan imposes a semi-permanent pressure minimum in the Santa Barbara Channel not associated with Santa Ynez Mountain lee side flow nor Catalina Eddies.

A detailed study is presented of two Catalina Eddies. The 19 June 1996 event that has a leading cloud edge that moves from the Eastern Southern California Bight along the coast to Point Conception. The 1 August 1996 event formed a cyclonic eddy exclusive of the Santa Barbara Channel area which had no clouds nor special wind shifts associated with a Catalina Eddy.

A new hypothesis on the cause of the Catalina Eddy is proposed. The mean, daily surface marine layer in the Southern California Bight south of the Channel Islands has a cyclonic distribution capped by a stable layer. An increase in mid-level cyclonic or decreased anticyclonic conditions that does not eliminate the stable layer capping layer can cause the surface layer to form a cyclonic eddy with a stratus overcast. This hypothesis satisfies all of the structural variation of eddies that are observed by satellite, the upper air stations and the dense network of surface stations around the Southern California Bight.

cat_eddy_final_2017.10.15_.pdf1.84 MB