Air-sea interaction observed by HF radar on Monterey Bay

Monterey Bay provides an interesting location for studying air-sea interaction under a cyclic, land-sea breeze, circulation in the atmosphere above the bay. The strong diuranal cycle allows investigation of the response of near-surface currents to large, periodic wind fluctuations. The observations used in this analysis were collected in the summers of 1997 and 2000. During both summers an air-sea measurement buoy M1 was active in the mouth of Monterey Bay and in 2000 a specially instrumented ´flux buoy´, FB, was also deployed in the east-central portion of Monterey Bay. Two multifrequency coastal radars (MCRs) operating at 4.8, 6.8, 13.4 and 21.8 MHz were sited at Moss Landing and Santa Cruz, California, collecting current maps at hourly intervals. We present observations and analyses in two areas: the center of the bay mouth (near the M1 mooring) and 8 km off the northeast shore of the bay (near the flux buoy FB mooring). These observations occurred during periods of strong land-sea breeze circulation in June of 1997 and Aug./Sept. of 2000. At the two buoy sites we study correlation between the surface wind vector and the current vectors at effective depths of about 0.5,, 1, 2 and 3 in as sensed by the different radar frequencies. We find the strongest correlation between the wind and the currents nearest the surface and that the surface currents are rotated about 40° clockwise (as seen from above) with respect to the wind vector, i.e. in the same sense as the Ekman spiral. We also study the spatial coherence of the surface current response to the surface winds