HR: 0800h
AN: OS21C-1251    [Abstracts]
TI: Unexpected tidal variation of the ocean-acoustic velocity
AU: * Sugioka, H
EM: hikari@jamstec.go.jp
AF: IFREE,Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Fukao, Y
EM: fukao@jamstec.go.jp
AF: IFREE,Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Hibiya, T
EM: hibiya@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033
AB: Ocean sound velocity significantly varies at tidal frequency in not only shallow but also deep pert. Unexpected largely semidiurnal fluctuation of ocean-acoustic waves (T-waves), which propagate through the SOFAR channel, is found on the ocean bottom seismometer records for the 1999 submarine volcanic swarm in northern Mariana. The amplitude is one order larger than any previous artificial experiments. Here we report the first in situ evidence that T-wave travel time provide information about vertical movement of seawater due to internal tides. Numerical 3-D modelling shows the internal tide excited by external tidal forcing is particularly large along the Izu-Bonin-Mariana Ridge because of rough topography. A semidiurnal up-and-down movement associated with the internal tide cause an undulation of the SOFAR channel on the order of 100 m, which causes T-wave travel time variations consistent with the observed ones. The results are consistent with the observed travel time variations both in amplitude and phase, demonstrating that T-waves from volcanic swarms can be used to detect oceanic internal tides. Generation of internal tides is an important sink of the external tidal energy so that accurate estimate of conversion of the external to internal tides is essential to close the global tidal energy budget and to understand the Earth-Moon system evolution.
DE: 4200 OCEANOGRAPHY: GENERAL
DE: 4560 Surface waves and tides (1255)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting