Toshiyuki Asano, Toru Yamashiro, Taro Kakinuma


Field observations on secondary oscillations (seiche) in Urauchi Bay of Kami-koshiki Island, Japan were conducted during October 7-21, 2008. The seiches prone bay has a unique configuration as T-shape, which may cause the inherent characteristics of the eigen oscillations. The analyzed data show that the oscillations of the bay have at least two distinct modes; mode-1 oscillation of the period around 25 minutes with forming anti-nodes at the both inward inlets and possessing a node at the bay mouth, mode-2 oscillation of the period around 12 minutes which oscillates between the both inward inlets having the node at the branching point. Next, numerical simulations were conducted to reproduce the secondary oscillations in the bay by providing input sinusoidal waves with the eigen periods of oscillations to the calculating bay geometry. The numerical results are found to show basically consistent characteristics with the field observations.


Secondary oscillation, seiche, coastal disaster, air-ocean coupling process, harbor resonance

Full Text:



de Jong, M. P. C. and J. A. Battjes (2004): Low frequency sea waves generated by atmospheric convection cells, J. Geophysical Res., Vol. 109, C01011, pp.1-18.

Hibiya, T. and K. Kajiura (1982) : Origin of the Abiki phenomenon (a kind of seiches) in Nagasaki bay, J. Oceanographical Society of Japan, Vol. 38, pp.172-182.

Shirahashi, T., T. Kakinuma, T. Asano and M. Sato (2008): Numerical simulation of long-period oscillation in a branching bay of Koshiki islands, Annual Journal of Coastal Engineering, JSCE, pp.216-220 (in Japanese).

Vilibic, I., S. Monserrat, A. Rabinovich and H. Mihonovic (2008) : Numerical modeling of the destructive meteotsunami of 15 June, 2006 on the coast of the Balearic Islands, Pure and Applied geophysics, Vol.165, pp.2169-2195.