Internal surges in coastal waters

A multiple element thermistor chain was installed at the end of Scripps pier in La Jolla, California, in 5 m of water along with a pressure sensor to record sea surface fluctuations. Temperature fluctuations throughout the water column are characterized by the occurrence of events, times during which a significant thermal gradient, of the order of or greater than those associated with the seasonal thermocline in deeper waters, exists in the water column. Temperature differences between the bottom and the surface of up to 5°C have been measured in events that are similar to those reported by Cairns (1967). The contributions of this work are to report (1) that the onset of events can be very rapid, occurring during times of the order of 1 s, (2) that motions exist in the water column at frequencies much higher than the buoyancy frequency that are not directly coupled to the surface wave field, and finally (3) that events are likely to be strongly three-dimensional in such shallow waters. Extrapolations of observations at Scripps pier on a worldwide scale indicate that such events could be responsible for an energy flux into shoal waters ranging between 2×105 kW and 2×107 kW, an estimate which is to be compared with the 2.5×106 kW proposed by Wunsch and Hendry (1972) on the basis of estimates of the power, in the form of internal waves, incident on the coastline of the world.