Harmonic Analysis of Solar Annual and Solar Semi-annual Tide in Japan

Abstract

It is a well known fact that the height of the mean sea level changes with the season of the year, and that the range of annual variation reaches even as large as 40 cm. at some parts along the Japanese coast. It reaches to the maximum height generally in late summer or in early autumn, and to the minimum in middle or late spring. These partial tides are called as " Solar annual tide " and " Solar semi-annual tide ", and are usually abbreviated as Sa and Ssa respectively. The causes of this annual variation have been considered to be attributed to the meteorological and oceanographical origins, and many authorities have tried to explain this phenomenon qualitatively and quantitatively, but this problem has not yet been definitely solved.Engaging in the routine work of tidal prediction in the past few years, however, the author has found that the amplitude of annual variations varies year by year, and he was interested in finding the sources of deviation of these annual variations compared to the mean amplitude for a long period at respective places.In this short report, however, I shall not go into the details of these discussions, but only show the results of the harmonic analysis based upon the observations as long a period as I could obtain. § 2 The method of obtaiping the data.The -data were all taken from the reports " Tidal Observations " published by the Marine Observatory, Kobe, Japan.In some tidal stations, the standard datum from which the height of the sea surface was reckoned, had been changed in the way of the observation period. In such cases, the whole data throughout the period can never be considered to refer to some definite levels.Thus, to reduce them to one definite level, the following corrections were aiplied to the respective period. The detail of the reason of these corrections will be seen in " Memoirs of the Fukuoka Meteordtogical Observatory," which will he published in the near future.Plotting the data obtained in this way on the graph paper in the chronological order, the author found that the yearly mean sea level undergoes some secular changes (see Fig.