Measurements of upper ocean surface current shear with high-frequency radar

Estimates of the variation with depth of both the speed and direction of nearsurface ocean currents within the top meter have been made using time series data collected from a dual-frequency, high-frequency radar located on the California coast, south of Monterey. Long-term averages derived from this data set over 3 different years consistently revealed an expected reduction in the speed of the near-surface current as a function of depth, consistent with a logarithmic vertical current profile. An unexpected and previously unmeasured clockwise rotation with increasing depth of the near-surface current was also observed. Hypotheses are suggested for the apparent rotation.