The initiation of high speed summer coastal winds along the US West Coast

The summer coastal winds off the US West Coast were examined with preliminary QuikSCAT, high resolution 12.5 km footprint scatterometer data. Great wind structure is in the coastal wind field that is due to hydraulic effects associated with coastal topography. Southbound, high-speed winds on the coast usually initiate at Cape Mendocino or less frequently, Cape Blanco. Both capes have large along coast and cross scales, with Cape Mendocino the greater in the cross-coast. Whichever cape initiates the fast flow, the fast flowing atmospheric marine layer generally continues along the coast to well south of Pt Reyes. A leading edge of high speed, southbound winds extends to the SW of the initiation cape. Hydraulic expansion fans further accelerate the marine air in the lees that are more localized in area. The smaller scale, downwind, but relatively close, Pt Area cape has southbound flow established by the upwind Cape Mendocino or Cape Blanco. In the inshore, there may be a high speed wind field extending directly from the Cape Mendocino expansion fan to past Pt Arena. The flow will be further accelerated in the Pt Arena lee, but is more limited in the cross and along shore extent. Farther offshore of Pt Arena, there may be weaker wind zone and then a stronger, wind speed zone. The effect is that the speeds of the southbound coastal marine layer approaching Pt Arena is established by the large, upwind capes of Mendocino or Blanco. There is a great temporal variation in the location, aerial coverage and speeds of the wind structure so that satellite tracks separated by day, or even a half day, are substantially different. Arial wind speed analysis over expended periods tend to wash out prominent coastal wind speed features in individual satellite passes.