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AbstractFor the purpose of enhancing the accuracy of tidal prediction, a review of the tidal harmonic constants and an examination of the number of constituents to be used for the prediction were studied by using the long~term observation data obtained at Kasima, Hirosima, Sibaura and Muroran. The results obtained are summarized as follows: The constituents of the short-period group can be satisfactorily determined to a certain degree even if they are computed from the data obtained from a one-year observation. However, taking into account such factors as synodic periods among different constituents, the existence of constituents corresponding to meteorological variations, etc., it is considered that tidal constituents should be determined from such data that make up the mean of those for several years. Since the amplitudes of the constituents of the long period group (Mm, Mf, MSf, Sa and Ssa) can be recognized as a composite of the constituents of astronomical tides and meteorological tides, they should necessarily be computed from the data obtained by longer period observations. These values are also obtainable from the values of daily mean sea levels for a long period. As for the number of constituents to be used for prediction, the accuracy in prediction stated in the Tide Tables would be retained even by those 38 constituents presently employed. However, these 38 constituents do not always correspond to the order of amplitudes of necessary constituents at individual places while local peculiarities may be seen in such an order. It also seems that accuracy in prediction tends to be raised approximately in proportion to the sum of amplitudes of constituents used. Taking the case of Sibaura for example, the following differences were found as compared to the actual observation data : In the case of using 38 constituents, the departure of tidal height is 6.9 cm on average with a standard deviation of 9.6 cm; the departure of tidal hour is 7.2 minutes on average with a standard deviation of 16.6 minutes. In the case of using 110 constituents, the departure of tidal height is 5.9 cm on average with a standard deviation of 8.7 cm; the departure of tidal hour is -0.9 minute on average with a standard deviation of 13.7 minutes. In conclusion, it can be said that the larger the number of constituents used, the higher the accuracy obtained in tidal prediction. Key words: Least square method 110 harmonic constituents. Accuracy of tidal predictions. Departure of tidal heights.
JournalReport of Hydrographic and Oceanographic Researches