SEA BREEZES SHALLOW AND DEEP ON THE CALIFORNIA COAST

Analyses of Doppler lidar data reveal sea breezes occurring on two dif ferent depth and time scales at Monterey Bay, California, on a day wit h offshore gradient flow indicated before sunrise and after sunset. Th e lidar data used in this study consist of vertical cross sections and profiles of the westerly, onshore wind component u. In the morning af ter 0900 PST a shallow sea breeze formed, which reached a depth of 300 m by noon. Starting in early afternoon a deeper sea-breeze layer form ed in the lowest kilometer, and by late afternoon the shallow sea bree ze blended into the deeper sea breeze and was no longer evident. Maxim um speeds of 6 m s(-1) in the shallow sea breeze occurred at the surfa ce, whereas those in the deep sea breeze (also 6 m s(-1)) were about 3 00 m above the surface. It is hypothesized that the shallow sea breeze is a local phenomenon responding to a more local temperature contrast between the sea and the region between the ocean and the mountain ran ges. The deeper sea breeze, on the other hand, is seen as a more regio nal circulation, driven by the larger-scale contrast between the atmos phere over the ocean and that over the hot interior valleys of Califor nia, or perhaps even a larger continental scale. The Lidar observation s also included the evening transition, which began as a very shallow land breeze observed only by surface observing stations. In the deep s ea-breeze layer between 250 m and 1 km AGL, the flow returned to offsh ore gradient flow simultaneously through the entire layer 2-4 h after sunset. The sea breeze was thus seen as a daytime interruption of the basic gradient offshore flow.