Neutrally buoyant current floats at depths between 500 and 2500 m at 28°12'N, 139°07'W and 28° 48'N, 117° 41'W exhibited a marked periodic motion. The floats moved in clockwise orbits at speeds of 5- 18 cm/sec and with a period of approximately 25 hours. The orbital is approximately equal to the inertial period. Floats tracked simultaneously at different depths were not in phase. With one exception, such motion has not been observed at other latitudes. It is believed that the observed motion was a result of internal waves and that such motions are restricted to a rather narrow belt of latitude.
Knauss, John A.. 1962. "Observations of internal waves of tidal period made with neutrally buoyant floats." Journal of Marine Research 20, (2). https://elischolar.library.yale.edu/journal_of_marine_research/977