Adjustment of the summer marine boundary layer around Point Sur, California

An instrumented C-130 aircraft hew over water around Point Sur, California, on 17 June 1996 under strong northwest wind conditions and a strong marine inversion. Patterns were flown from 30- to 1200-m elevation and up to 120 km offshore. Nearshore, marine air accelerated past Point Sur, reaching a s urface maximum of 17 m s(-1) in the lee. Winds measured over water in and a bove the marine layer were alongshore with no significant cross-shore flow. Sea level pressure, 10-m air temperature, and air temperature inversion ba se generally decreased toward the coast and were an absolute minimum just d owncoast of the wind speed maximum. The sea surface temperature also decrea sed toward the coast, but was an absolute minimum directly off Point Sur. T he neat: coast, air temperature inversion base height was 400 m north of Po int Sur, decreased to a minimum of 50 m in the lee of Point Sur, then incre ased farther to the south. Wind speeds were at a maximum centered along the air temperature inversion base; the fastest was 27 m s(-1) in the lee of P oint Sur. Using a Froude number calculation that includes the lower half of the cappi ng layer, the marine layer in the area is determined to have been supercrit ical. Most of the marine layer had Froude numbers between 1.0 and 2.0 with the extreme range of 0.8-2.8, Temperatures in the air temperature inversion in the lee were substantially greater than elsewhere, modifying the surfac e pressure gradient. The overall structure was a hydraulic supercritical ex pansion fan in the lee of Point Sur under the influence of rotation and sur face friction. The Naval Research Laboratory nonhydrostatic Coupled Ocean/Atmosphere Mesos cale Prediction System (COAMPS) indicated a broad, supercritical marine bou ndary layer moving to the south along central California and Point Sur duri ng the aircraft flight. The marine boundary layer thinned and accelerated i nto the lee of Point Sur, which was the site of the fastest sea Level wind speed along central California. Isotherms dip and speeds decreased in the l ee of Point Sur in the capping inversion well above the marine layer. COAMP S forecasted a compression shock wave initiating off the upwind side of the topography behind Point Sur and other coastal points to the north. Evidenc e from the model and the aircraft supports the existence of an oblique hydr aulic jump on the north side of Paint Sur.