32nd Conference on Broadcast Meteorology/31st Conference on Radar Meteorology/Fifth Conference on Coastal Atmospheric and Oceanic Prediction and Processes

Wednesday, 6 August 2003: 1:30 PM
The effect of flow over coastal topography on the character of low-level offshore wind maxima along the California coast in summer
Patrick S. Cross, U.S. Navy, Pearl Harbor, HI; and D. K. Miller and W. A. Nuss
Poster PDF (926.2 kB)
COAMPS model results along the coast of California are examined with the goal of determining the dynamics involved in the formation of the low-level wind maxima that occur in the lee of significant coastal prominences. These features have generally been described as being primarily caused by supercritical flow expansion as low-level coast-parallel winds encounter a turn in the coastline away from the flow. Results from this study indicate that flow above the marine layer, and thus outside the supercritical channel, plays a substantial role in defining the character of the offshore wind maxima within the coastal jet, which typically occur within the inversion at the top of the marine layer. Specifically, as roughly coast-parallel flow above the marine layer encounters one of six significant mountain areas close to the coast, a mountain wave response occurs. This produces an area of reduced low-level pressure in the lee of coastal topography over water as the inversion is compressed and as flow down the mountain is warmed adiabatically. This effect generally works in concert with supercritical expansion, since in each case the high coastal terrain is in close proximity to some degree of coastal turn. When flow above the marine layer is light, or exhibits too great an onshore component, the low-level wind response downwind from the coastal feature is limited in scale and magnitude and appears to be due only to the expansion effect. However, as flow speeds increase above the marine layer, the mountain wave effect becomes more prominent, increasing the magnitude of the low-level maximum and expanding its scale further offshore and downstream from the associated coastal mountain. It is the offshore extension of these waves at a characteristic angle to the coast that appears to account for the broad scale of the low-level wind maxima on days when coastal jet winds are well developed.

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