Coastal Eddies in the Ocean Wind Field as Observed by Single and Multifrequency HF Radars on Monterey Bay, California

Coastal wind eddies at the 10-40 km scale have been studied over Monterey Bay, California by Archer, Ludwig et al. using shore and buoy anemometers and satellite images. Most frequent in the evening and early morning hours, these, typically cyclonic, eddies are often responsible for fog in the Santa Cruz area. We have previously demonstrated the ability of multifrequency HF radar (4.8 to 21.8 MHz) to map the ocean wind field. Observations over a year time span indicate standard errors of prediction of 1.7 m/s for wind speed and 25deg for direction with biases of 0.1 m/s and 0.3deg respectively. By combining HF radar wind vector estimates with shore based anemometer data in the WOCSS surface wind field model we are able to form detailed (3 to 5 km resolution) images of eddies over Monterey Bay and to follow their development and decay. We discuss the requirements for making wind field maps with HF radars and demonstrate how the changing array of multiple radar sites can be used to produce HF radar wind field maps. We report observations of 10-20 km cyclonic eddies in the northern and eastern parts of Monterey Bay.