Observations of near-surface ocean currents at varying depths using a new multifrequency HF radar

Abstract

A new multifrequency (4-25 MHz) HF radar was installed at the Long Marine Lab. (University of California at Santa Cruz) on the north coast of Monterey Bay CA in July, 1996. This radar is capable of observing near-surface currents at varying depths in the top two meters 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. Fourier analysis of these data shows 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 deeper current measurements from buoys and moorings are able to investigate the upper layer of the coastal ocean where wind and tidally driven currents struggle for dominance.