Observing Eddy Features in the Ocean Surface Wind Field by Assimilating HF Radar and Anemometer Measurements in a Wind Model

Strong evidence for 10-40 km scale eddies in the surface wind field over Monterey Bay, California has been presented by Archer, Ludwig et al. using shore and buoy anemometers and satellite images. These cyclonic eddies are frequently present in the evening and early morning and are 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. Here we report observation of a 10-20 km cyclonic eddy at the north end Monterey Bay. By combining HF radar wind vector estimates with shore based anemometer data in the WOCSS surface wind field model we are able to form a detailed (5 km resolution) image of an eddy over Monterey Bay and to follow its development and decay. This particular eddy contrasts with previous eddy observations in terms of season and meteorological setting.