Observations of currents from the near-surface to 50 m depth using a new multifrequency HF radar and an ADCP located in the radar observational area

In July 1996 a new multifrequency (4-25 MHz) HF radar was installed at the Long Marine Laboratory (University of California at Santa Cruz) on the north coast of Monterey Bay. This radar is capable of observing near-surface currents at varying depths in the top two metres of the ocean. Observations were made over a ten-day period in March 1997 during which there was a strong land-sea breeze circulation over Monterey Bay. Radial current measurements corresponding to depths of about 0.3, 0.5, 1.0 and 1.4 m were made during this period using HF radar data from four operating frequencies. Acoustic Doppler Current Profiler (ADCP) measurements were made at the MBARI M1 buoy near the mouth of the bay. Time series and Fourier analyses of these data show that very near the surface the strongest periodic component is a diurnal one corresponding to the diurnally varying surface stress from the land-sea breeze. At deeper depths the diurnal component remains, but a semi-diurnal component grows in strength with increasing depth of the current measurement. Thus, multifrequency HF radar combined with current measurements from buoys and moorings can investigate the air-sea interaction from within about 30 cm of the surface to depths of 50 m and more.