U. S. West Coast

Project

A continuous series of 12-hr COAMPS forecasts have been run over the U.S. west coast region beginning October 1998.  Every 12 hours the forecasts are incrementally updated with standard adp observations and an ocean analysis is performed at grid resolution.  From the hourly forecast fields, vertical profiles of modified refractivity are computed and averages of ducting characteristics on the 9-km inner nest 3 are obtained from selected months during each season of 1999. 

Results

Figure 1 shows the monthly averaged duct strength and duct base height for January, April, July and October of 1999.  In addition to the spatial variability apparent in these mean fields, the patterns indicate seasonal transitions.  Color shading of duct strength (DS) show that the strongest ducts occur in the Southern CA Bight and in the month of October (DS_max = 28 M-units) while the north coast (OR/CA boarder) has much weaker ducts especially in spring and summer (DS_min= 5 M-units compared to DS_max= 12-16 M-units offshore and in the Bight).  Duct base heights (DBH) slope up away from the coast with surface based ducting more likely along the north coast and elevated ducts in the SW part of the model domain (near 30°N, 130°W).  In fall/winter the slope is greater than spring/summer with a tendency for surface-based ducting from Cape Mendocino to northern OR sloping to an offshore DBH in the SW near 300 m.  In spring and summer, coastal DBH are near 100 m sloping to an offshore height in the SW near 200m.