CURRENTS OBSERVED NORTH OF OAHU DURING THE FIRST 5 YEARS OF HOT

Shipboard ADCP sections from 30 Hawaii Ocean Time-series cruises over a 5-year period show a mean flow 15 degrees north of west, reaching a maximum of 17 cm s(-1) about 50 km north of Oahu. This North Hawaiian Ridge Current is highly variable from cruise to cruise and from year t o year. It was generally strong in the sections 1988-1991 and weak or absent in 1992 and 1993. There is no prominent annual cycle. Unresolve d short-period oscillations are so energetic as to obscure the mean cu rrent in individual sections. The 5-year mean is highly significant, h owever, at five times the estimated standard error. Currents also were measured with a shipboard ADCP during the nominally 3-day occupations of the HOT Station ALOHA. The mean over 32 cruises was near 6 cm s(-1 ) in magnitude at all depths from 20 to 200 m, but the median was near zero. Hence, the northern boundary of the North Hawaiian Ridge Curren t was usually south of ALOHA. The inter-cruise standard deviation of v elocity varied from 22 cm s(-1) at 20 m to 11 cm s(-1) at 200 m for th e zonal component, and 13 cm s(-1) to 8 cm s(-1) for the meridional co mponent. Intra-cruise variability during the 17 cruises with the best sampling in depth and time was dominated by a linear trend, near-inert ial oscillations, and diurnal and semidiurnal tides. Each of these fou r elements had an rms value near 6 cm s(-1) at 20 m, decreasing to 2-4 cm s(-1) at 250 m. The vertical shear field was dominated by the diur nal tide and near-inertial oscillations; the semidiurnal tide and the trend had larger vertical scales of variability and consequently made smaller contributions to the shear. Copyright (C) 1996 Elsevier Scienc e Ltd