Observations of internal tides in October 1950*

Over six days of anchor station hydrographic data from each of three vessels on a line 280 mi long were analyzed for internal waves of tidal (and other) periods. Waves of semidiurnal period with amplitudes greater than 30 ft were found at the nearshore station (40 mi offshore in 1080 fm), but little evidence of these waves or any other periodic phenomena was found at the stations farther offshore though there was considerable vertical fluctuation of isotherms. It is suggested that the waves found originate near the coast in the action of the surface tides and that, since the length of such waves, if free, is short, they either dissipate before proceeding far offshore or, more likely, are so distorted by the varying density structure and water velocity that they are no longer recognized.