2005 Fiscal Year Final Research Report Summary
Quantitative evaluation of the exchange processes of momentum and seawater associated with Kuroshio frontal waves
| Project/Area Number |
15540421
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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 |
ISOBE Atsuhiko Kyushu University, Interdisciplinary Graduate School of Engineering Sciences, Associate Professor, 大学院・総合理工学研究院, 助教授 (00281189)
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| Project Period (FY) |
2003 – 2005
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| Keywords | Kuroshio frontal eddies / East China Sea / subsurface intrusion / alternating bands of mean currents / diffusive stretching / topographic Rossby wave / resonant interaction |
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| Research Abstract |
First, a two-layer numerical model is used to investigate the continental-shelf circulation forced by western boundary currents along shelf edges. After long-term integration, the model reaches the equilibrium state in which alternating bands of long-term mean currents are found over the continental shelf. The western boundary current is accompanied by frontal waves, and so vertical momentum transfer occurs because of to the diffusive stretching. Topographic Rossby waves are excited on the shelf slope by the vertical momentum transfer. Thereafter, energy of the waves proceeds to flow toward the lower-frequency limit by resonant interactions. The along-shelf wavenumber also vanishes to satisfy the dispersion relation of the topographic Rossby wave. As a consequence, the alternating bands of mean current are found over the continental shelf.
Second, the possible origin and cause of the less saline shelf water detected in the Kuroshio subsurface layer around the shelf edge of the East China Sea are investigated using observational results obtained in May 1998-2001 in conjunction with a numerical model. The observations show that subsurface intrusions of less saline water are always detected in May in layers above 24.5 σ_θ isopycnal surface, and that salinity inversions are detected around the trough of the Kuroshio frontal eddy (or wave). Numerical models demonstrate that, when the frontal wave captures the less saline water, the shelf water takes the form of a salinity inversion in the trough because isohalines in the frontal wave have a phase lag between the upper and lower layers in consequence of the baroclinic instability.
Third, this study also provides a physical interpretation for the ballooning of river-plume bulges by conducting numerical experiments in which a river plume is induced by a coastal freshwater source.
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