Thursday, 7 August 2003: 8:00 AM
Evaluation of high resolution model surface winds and their effect on wave model performance over the Southern California bight
Ever increasing spatial resolution in atmospheric models has led to significant improvements in modeling ocean-atmosphere processes. This is especially true in coastal zones, where relatively high resolution is often necessary to simulate processes that directly depend on coastal geometry and topography. However, increased spatial resolution does not necessarily imply increased accuracy; there is still a need for careful verification of model fields. Surface winds from NOAA National Centers for Environmental Prediction Eta-12 regional model (run operationally by NCEP every 6 hours) is compared with observations in the coastal ocean of the Southern California bight. The comparisons focus on periods of relatively strong northwesterly winds, which are due to a combination of synoptic forcing, a shallow atmospheric subsidence inversion, and complex coastal geometry and topography. Wind speeds frequently exceed 15 m/s at the mouth of the Santa Barbara Channel, especially in spring and summer. These winds produce hazardous seas that pose risks to commercial, recreational, and naval operations throughout the Southern California bight.
A preliminary comparison of model winds with buoy measurements during northwesterly wind events in November 2002 may suggest a low bias in Eta-12 surface wind speed in the Southern California bight. For the November northwesterly wind events, a simple linear bias adjustment showed marked improvement compared with several buoys in the bight. The possibility of a low bias in surface wind in the Southern California bight will be further explored during northwesterly wind events this spring and summer of 2003.
Additionally, the Eta-12 winds have been used to drive a 5-km nested ocean wave model configured over the bight (WAVEWATCH-III available from NOAA/NCEP). We examine wave model performance with the inclusion of Eta-12 winds. Details on the wave model configuration and more general comparisons of significant wave height and wave period from observations with wave parameter estimates from the nested model are discussed in a companion presentation.