THE ACCURACY OF TIDE-GAUGE MEASUREMENTS AT SUBTIDAL FREQUENCIES

The accuracy of subinertial sea level, as measured by tide gauges in t he Southern California Bight, is investigated. Sea level differences f ormed from tide gauges separated by less than 50 km are examined. The observed differences give an upper bound on errors in the sea level da ta, provided errors at each station are uncorrelated with each other a nd with the true sea level signal. Sea level measurements at the San D iego and La Jolla tide gauges are also compared with simultaneous bott om pressure measurements made on the shelf 25 km north of San Diego. B oth comparisons suggest that rms errors in tide-gauge measurements of sea level are order 1.5 cm. Approximately half the observed error vari ance has time scales of 1 month and is due, in part, to inaccuracies i n determining reference levels.