Analysis of Freak Wave Measurements in the Sea of Japan

Nobuhito Mori ¹ , Paul C. Liu² and Takashi Yasuda ³

Abstract:

This paper presents an analysis of a set of available freak wave measurements gathered from several periods of continuous wave recordings made in the Sea of Japan during 1986 - 1990 by the Ship Research Institute of Japan. The analysis provides an ideal opportunity to catch a glimpse and statistics of freak waves in the ocean. The results show that a well-defined freak wave may occur in a developed wind wave condition: $S(f)\propto f^{-4}$ with a single peak directional spectra. The crest and trough amplitude distributions of the observed sea waves including freak waves are different from the Rayleigh distribution, although the wave height distribution tends to agree with the Rayleigh distribution. Freak waves can be readily identified from the wavelet spectrum where strong energy density in the spectrum and are instantly surged and seemingly carried over to the high frequency components at the instant the freak wave occurs.