超音波流速計による砕波帯における長期連続観測

Abstract

A series of long-term observations of nearshore currents have been carried outat Ogata Coast using ultra-sonic current meters (USC) mounted on Ogata WaveObservatory's T-shaped observation pier. The USC's noise reduction circuit wasimproved for remarkable noise caused by air bubbles and suspended sand which areintroduced by breaking waves.Continuous USC's records reveal some characteristics of the nearshore currents(NSC) at Ogata Coast, they include:1) The tidal flow is weak and the influence of wind is very large.2) The typical relation between the winter monsoon and the NSC has beendetermined. Then the monsoon occurrs, wind and waves come from the westdeveloping the NSC as the longshore current which flows to the east. The windthen comes from the east, or becomes weak, and waves come from the east, theirperiods increase, and the NSC becomes from the longshore current to the offshorecurrent.3) Within the surf zone, this strong offshore current has a homogeneousvelocity profile from the surface to the bottom.