Large-scale structure of the June-July 1996 marine boundary layer along California and Oregon

Data from surface stations, profilers. lone-range aircraft surveys, and sat ellite!, were used to characterize the large-scale structure of the marine boundary layer off of California and Oregon during June and July 1990. To s upplement these observations, June-July 1996 averages of meteorological fie lds from the U.S. Navy's operational Coupled Ocean-Atmospheric Mesoscale Pr ediction System (COAMPS) model were generated for the region. Model calcula tions show a broad band of fast northerly surface winds exceeding 7 m s(-1) extending along the California-Oregon coast. Buoy-measured peaks of 7.1 m s(-1) off Bodega Bay, 7.2 m s(-1) off Point Piedras Blancas, and 8.8 m s(-1 ) near Point Conception were reported. Mean winds at the buoys located 15-2 5 km offshore ore generally faster than those at coastal stations, and all station winds are faster in the afternoon. The aircraft and station observations confirm that an air temperature inver sion typically marks the top of the marine boundary layer, which deepens of fshore. Along the coast, the marine boundary layer thins between Cape Blanc o and Santa Barbara. The inversion base height is at it, lowest (195 mn) at Bodega Bay in northern California and at its highest at Los Angeles and Sa n Diego (416 m). The inversion strength is strongest between Bodega Bay and Point Piedras Blancas, exceeding 10.8 degrees C. The June July 1990 marine boundary layer depth from COAMPS shows a gradual deepening with distance o ffshore. The model-averaged Row within the marine boundary layer is supercr itical (Froude number > 1) in a region between San Francisco and Cape Mendo cino that extends offshore to 126.4 degrees W. Smaller isolated supercritic al areas occur in the lee of every major cape, with the peak Froude number of 1.3 in the lee of Cape Mendocino. This is consistent with aircraft Right s of Coastal Waves '96, when extensive regions of supercritical flow off ce ntral California and downwind of major capes were recorded with highest Fro ude numbers around 1.5-2.0. A broad, wedge-shaped area of nearly critical f low (Froude number > 0.8) extends from Cape Bianco to Point Piedras Blancas and offshore to about 128.5 degrees W in the model output. The model wind stress has a broad maximum exceeding 0.3 N m(-2) between Cap e Mendocino and San Francisco with the highest values found within 100 Isn of the coast. Stress calculated directly from low aircraft legs is highest in the lee of large capes with peak values exceeding 0.7 N m(2). Overall ai rcraft magnitudes are similar to the model's, but a direct comparison with the 3-month average from the model is nor possible due to the lesser space and time coverage of the Rights. The stress maxima along the California coa st shown in the model results are spatially consistent with the region of c oldest sea surface temperature observed by satellite.