2006 Fiscal Year Final Research Report Summary
Fundamental research on the western boundary current induced by Rossby waves
| Project/Area Number |
16540401
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Meteorology/Physical oceanography/Hydrology
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| Research Institution | Kyushu University |
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Principal Investigator |
WAKATA Yoshinobu Kyushu University, Research Institute for Applied Mechanics, Professor, 応用力学研究所, 教授 (90201871)
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| Co-Investigator(Kenkyū-buntansha) |
IGA Keita University of Tokyo, Ocean Research Institute, Associate Professor, 海洋研究所, 助教授 (60292059)
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| Project Period (FY) |
2004 – 2006
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| Keywords | Kuroshio volume transport / Rossby wave / TOPEX / POSEIDON / Equatorial wave / East China Sea |
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| Research Abstract |
We investigate the interannual variability of Kuroshio volume transport using Ocean General Circulation Model and satellite altimeter data. It was found from the analysis in the middle latitude area that the Kuroshio volume transport can be understood from the propagation response of the baroclinic Rossby waves to the sea surface wind stress. However, this explanation was inapplicable in the area existing subtropical countercurrent owing to the effect of unstable waves.
The headstream of Kuroshio Current continues to the north equatorial current in the area of which it was known that there are many equatorial waves such as Rossby wave and Kelvin wave. These waves may influence this headstream. The sea surface height (SSH) anomaly was separated into equatorial modes using satellite altimeter data. The power-spectral density (PSD) was obtained for the east-west wavenumber and frequency for each separated mode. The PSD distribution was compared with the theoretical dispersion curve for the
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equatorial modes derived by Matsuno (1966). The first Rossby modes have a high-density distribution that is slightly lower than the theoretical dispersion curve, but the Kelvin mode and the higher Rossby modes have high-density distribution that almost matches each dispersion curve. Results of analyses of satellite observational data show that wave motion near the equator mainly shows characteristics of equatorial waves, especially for a intraseasonal time scale.
Seasonal variability of SSH in the East China Sea and the Yellow Sea was investigated through the study of model simulation and analysis of observed data. The model SSH was compared with the tide-gage data. The model SSH is also compared with the satellite altimeter data using Harmonic analysis, and they generally showed good agreement in wide area. The SSH is high in summer and low in winter. As a factor of this seasonal variability, SSH variability due to the thermal expansion was considered. The minimum appears in February and the maximum appears in September. However, the fluctuation range of model and altimeter data is about twice of this thermal expansion effect, and the time when the minimum appears is locally different. The dynamical effect due to the wind stress must be important. Winter monsoon burst extrudes the seawater from the northern marginal sea area. This may enhance the amplitude and advance the phase in this area. Less
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