Fluctuations in geopotential anomaly at eight 12-hr time-series stations off Washington appeared to result from semi-daily internal tides propagating seaward from the shelf break. Comparison of the observations with computations suggests the existence of a first mode wave. The oscillations did not appreciably decay offshore, perhaps as a result of bathymetric focusing.
Mofjeld, H. O., and R. K. Reed. 1978. "Semi-daily fluctuations in geopotential off the Washington coast." Journal of Marine Research 36, (3). https://elischolar.library.yale.edu/journal_of_marine_research/1441