Results of Simultaneous Observation of Secondary Undulation in Aburatsubo Bay

Abstract

In order to investigate the state of the seiche, a simultaneous observation of the secon dary undulation was carried out at six stations around and near Aburatsubo Bay, for the period from Feb. 11 to Mar. 27, 1958. In addition, atmospheric pressure and wind in the area were incessantly recorded throughout above mentioned period. The following conclusions were obtained by the investigations. (1) The observed periods of the seiche for both branched bays, Moroiso and Aburatsubo, are 13.515.5 min much the same for both bays, while their theoretical values are 12.8 min and 14.0 min respectively. The variation of the period seems to be due to the unsteadiness of the nodal line. (2) In winter, the seiche most frequently rises immediately after W- or WSW-wind that blows for 1020 hours, 58 (Beaufort) in force suddenly changes its direction or dec reases its force in short time. In view of above phenomenon, when the water at the end of the bay that was risen by the W- or WSW-wind-the upheaval amount of the sea level is about 12 mm per m/secin WSW-wind-returns to the normal state for sudden change of the wind, perhaps the moving of the water resonates to the proper period of the bay, then the seiche will be enforced.