On the Result of Wave Observations at Jogashima Island and Its Application to Wave Forecasting (I)

Abstract

Some investigations wer e made on the wave height and wave period of wind waves and swells, based on the data of. continuous observation of ocean waves with a self-registering wave gauge at Jogashima Island, Kanagawa Prefecture, Japan, duriug a year from September,1951 to August,1952, and the characteristics of variations of wave height and wave period and their relations to meteorological conditions were made clear. These results of analysis are also available for forecasting ocean waves. The variations of wave height and wave period can be classified into six types as shown schematically in Fig.5, and each of these types corresponds to a particular meteorological change. The points which have become known up to now are as follows:
1) In case a cyclone m oves eastward on the Pacific side of Honshu, Japan, the change of wave of “Type I” or“Type II” occurs at Jogashima Island, and the positions of the cyclonic centre at the time when the waves begin to become high, at the time when the wave height becomes maximum and at the time when the waves begin to decay at Jogashima Island are shown in Fig.8. Again, the positions of the cyclonic center at the time when the wave period becomes maximum are shown in Fig.9, Further, the maximum wave height, the duration of higher waves, etc. and their relations to the intensity and distance of the cyclone are shown in Figs.10-12.
2) In case a cyclone moves eastward on the. tapan Sea side of Honshu, the change of waves of “ Type III ” or “Type IV” occurs at Jogashima Island, and the maximum wave height, the duration of higher waves, -etc. in thaC. ca'se, are shown in Figs.,16-19.
3) In case a migratory anticyclone covers Honshu, the change of waves of “Type V” or “Type VI” occurs at Jogashima Island. And Fig.23 shows the extent of area covered by this migratory anticyclone when the sea is calm at Jogashima Island.
4) I n case the station under consideration is within the sphere of influence of Ogasawara Anticyclone, the change of waves is complicated, depending upon the nature of the sphere of influence. In this case, the change of waves of “Type V”or “Type VI” generally occurs, with incidental occurrence of the change of “Type III”. And we can see from Fig.25 the extent of area under the influence of this anticyclone when the sea is calm at Jogashima Island.