La mer
Online ISSN : 2434-2882
Print ISSN : 0503-1540
Volume 56 , Issue 3-4
Showing 1-3 articles out of 3 articles from the selected issue
  • Shiro IMAWAKI, Kenzo TAKANO
    2018 Volume 56 Issue 3-4 Pages 67-94
    Published: 2018
    Released: May 19, 2021
    JOURNALS OPEN ACCESS
    Observations by moored current-meters were carried out repeatedly in mid-ocean of the western North Pacific, providing 50 velocity records. A continuous velocity record for almost seven years was obtained at 5000 m depth. The overall mean velocity is directed to the north with a speed of less than 1 cm s-1. The kinetic energy of low-frequency velocity fluctuations, or mesoscale eddies is more than 30 times larger than that of mean flow. Frequency spectra of eddy kinetic energy show that most of the energy is contained in mesoscale bands (periods of 31-235 days), with zonal(meridional)dominance of energy in the longer(shorter)period band. An array observation at 4000 m depth shows that the local change of relative vorticity of mesoscale eddies is balanced mainly with the advection of planetary vorticity, although the horizontal advection of relative vorticity and higher-order horizontal divergence may play some role. Those results suggest that the mesoscale eddies are understood as primarily plane barotropic Rossby waves with possible modification.
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  • Mizuki KUGA, Yosuke IGETA, Naoki HIROSE, Tatsuro WATANABE
    2018 Volume 56 Issue 3-4 Pages 95-111
    Published: 2018
    Released: May 19, 2021
    JOURNALS OPEN ACCESS
    Characteristics of near-inertial fluctuations generated by typhoon in and around Toyama Bay(TB)that opens its mouth toward the north were investigated by using results calculated by high-resolution nested ocean model which is usually operated for fisheries. From harmonic, spectral and vertical-mode decomposition analysis, we confirmed that density and current fluctuations were fundamentally characterized by propagation of coastal-trapped waves(CTWs)generated at seamount adjacent to the land tip of Noto Peninsula(NP)that is western boundary of the TB. This result in counterclockwise phase distribution in density fields. Near-inertial internal waves(NIWs)were also generated around land tip(Nyuzen)located at the eastern boundary of the TB through topographical scattering processes of the CTWs. The NIWs propagated the northwestward by way of center of the TB, finally were reflected along the eastern coast of the NP toward the northeast. The NIWs formed clockwise phase distribution in current fields, which is opposite properties against that by the CTWs. The region of strong currents confirmed around the Nyuzen was considered to be resonant-amplification of currents of the CTWs and inertial oscillations.
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  • Tomoharu SENJYU, Jiro YOSHIDA
    2018 Volume 56 Issue 3-4 Pages 113-123
    Published: 2018
    Released: May 19, 2021
    JOURNALS OPEN ACCESS
    In this study, we revisited the rotating-tank experiments reported by FALLER(1960) and SENJYU(1988)and qualitatively discussed the abyssal circulation in the Japan Sea by focusing on the geometric similarity of their partial barrier experiments. A point source of water near the apex of the pie-shaped rotating-tank formed the so called STOMMEL-ARONS type circulation pattern. The circulation in the partial barrier experiments basically consisted of a cyclonic circulation and a western boundary current in the southern two basins separated by a partial barrier extending from the rim. Recent observations on direct current in the abyssal Japan Sea have revealed a cyclonic circulation and strong currents near the western boundary in the southern two basins: the Yamato and Tsushima Basins. These similarities suggest the STOMMEL -ARONS type circulation in the abyssal Japan Sea, though the complex bottom topography and eddy activity are likely to modify the basic circulation pattern significantly.
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