A brief method applied for the long-period tides Sa and Ssa, and the results by means of this method.

Abstract

The tidal harmonic constants for a port are expected to be nearly constant as long as the topography of the port was not extremely changed. It has been, however, shown by the calculated results up to date (Journal of the college of science, Imperial University, Tokyo Vol. 28, Article 7) that the harmonic constants vary by the changes in the astronomical, meteorological and oceanic conditions, etc. Especially, the variation of the long-period tides is more remarkable than others. Accordingly, in order to obtain more reliable harmonic constants of the long-period tides which can be adopted for tidal prediction, we should not calculate them from the results of observations for only one year, but from those for several years, However, it is too laborious and inefficient to carry out many times harmonic analysis such as the T, I, method or Darwin method, when the principal purpose is in obtaining long”period tides. Therefore, the brief method which obtains long-period tides Sa and Ssa by using twelve values of monthly mean sea levels for a year or several years will be described in this report. This method is the one obtaining the six unknowns by means of the method of least sqares on the assumption that a curve which is drawn by twelve values of monthly mean sea levels of successive years or of a year consists of the six terms, i, e, constant, linear term concerning time and cosine and sine terms of the product of time and phase-increment per a solar day of Sa and Ssa. Using this method, we may also deduce the secular variations of ground or sea level. Moreover, in this report the harmonic constants, which have been calculated by means of this method, of long-period tides Sa and Ssa will also be included for 74 ports along the coasts of Japan.