Tuesday, 11 February 2003
Wind divergence forcing of the cloudiness along the California coast
Numerical experiments were made using Mesoscale Model 5 (MM5) with a horizontal resolution of 9 km to simulate the wind divergence along California and Northern Baja California for all of June 1996. Theory supports, and comparison with satellite cloud images confirms, that marine layer wind divergence causes the lowering of the marine layer and an associated decrease in cloud cover. Marine layer convergence/divergence and cloud structure are greatly affected by the topography along the coast of Southern California and Northern Baja California. Point Conception has a dramatic effect on the southbound summer marine layer. The flow slows on the upwind side and accelerates around the point into the close and immediate lee in the western mouth of the Santa Barbara Channel. However, over the scale of the Southern California Bight, the Cape forces the winds to turn eastward and slow. The result is an increased marine layer depth and clouds in the main area of the Southern California Bight. There is considerable cloud structure in the lee of islands that extends great distances downwind. Point Conception's lee effects end north of Ensensada. By Ensenanda, the marine layer flow intensifies and again becomes parallel to the coast. The divergence and convergence zones with associated marine layer depth and cloud variations are found along northern Baja California that are similar to those found along the Central California coast.