A Study on Long Period Waves in Coastal Waters of Toyama and Niigata

The research on waves has been carried out in National Institute of Technology,Toyama College(NIT,Toyama College)since 1967,but generating mechanism of long period waves is not clear yet.And so,long period waves were investigated by analyzing tide levels which were observed at coasts of Toyama and Niigata in this study.The results are as follows. (1)There is a wave with period of about 321 days in residuals between observed and calculated tide levels,amplitude and phase of the wave in Toyama and Niigata are the same.The amplitude of the wave is 1.5cm and the phase of the wave is 284 degrees. (2)There is a wave with period of about 420 days in residuals between observed and calculated tide levels,amplitudes and phases of the wave in Toyama and Niigata are slightly different from each other.The amplitude of the wave is 1.3 cm in Toyama and 1.2 cm in Niigata and the phase of the wave is 263 degrees in Toyama,260 degrees in Niigata. The wave with period of about 321 days,amplitude of 1.5 cm and phase of 284 degrees,which exists in coastal waters of Toyama and Niigata,is generated by fluctuation of the earth gravity.Further there is a possibility that the wave with the period of about 420 days,which corresponds to chandler period(about 435 days),is driven by the polar motion.Moreover,the waves suggest that tectonic plates are swaying relatively to inner earth under asthenosphere,and as a result,gravity on earth surface fluctuations with periods of 321 days and 420 days. It is a future problem to make clear generating mechanisms of the long period waves.