Features of the Wave Processes in the South Kuril Strait Based on Observational Data

Purpose. The work is purposed at studying the waves in the South Kuril Strait within the period ranges from the wind waves to the tidal ones using the field observations data, and also at explaining the observed wave processes using the existing theories and models. Methods and Results. The results of the analyzed long-term (up to 12 months) time series of observations of waves and water temperature performed with the 1 s discreteness by the bottom autonomous wave recorders ARW-K14 at three points in the South Kuril Strait coastal zone are considered. To detect wave processes, the spectral analysis was applied. It showed the presence of significant maxima in the spectral densities that resulted in revealing the diurnal and semidiurnal tidal waves, and the time series of seawater temperature fluctuations made it possible to find out the waves with a period of the tidal harmonic K1. The seiche periods were calculated by the formula for a semi open water area, and it showed the possibility of generating eigen oscillations of sea level in the South Kuril Strait with a period 5.0 hours, which was close to the period 4.8 hours derived from the observational data. It was revealed that the seiches amplitude are increased after the ebb reached its minimum level and further as the level grew. This effect (described by D. K. Chapman and G. S. Giese in their articles) is explained using the dynamic mechanism of generating the coastal seiches by deep-sea internal waves induced by a barotropic tide.Conclusions. It is shown that both seiches and tidal harmonics can contribute energy to the wave process with a period 4.8 hours. The level fluctuations with the periods varying from 0.4 to 3 hours do not depend on tidal harmonics and, possibly, they are the seiches or the edge waves. The results of a spectral analysis of three time series permitted to find out that seiches in the South Kuril Strait were of low energy and there were no conditions for their significant resonant amplification. It was shown that a part of the energy of tidal waves was transferred to the seiche oscillations in the Krabovaya and Malokurilskaya bays. Having being analyzed, the sea level fluctuations in the range of infragravity waves showed the possibility of the South Kuril Bay fluctuations to transform to the chaotic ones, which had been confirmed by modeling the behavior of the dynamic system - the water mass of the bay excited by the incoming swell waves.