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Form drag in quasigeostrophic flow over sinusoidal topography

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Title: Form drag in quasigeostrophic flow over sinusoidal topography
Other Titles: サイン型地形上を流れる準地衡流における形状抵抗
Authors: Uchimoto, Keisuke1 Browse this author
Authors(alt): 内本, 圭亮1
Issue Date: 30-Jun-2004
Abstract: The relationship between form drag and the zonal mean velocity in steady states is investigated in a very simple system, a barotropic quasi-geostrophic channel with a sinusoidal topography. When a steady solution is calculated by the modi ed Marquardt method keeping the zonal mean velocity constant as a control parameter, the characteristic of the solution changes at a velocity. The velocity coincides with a phase speed of a wave whose wavenumber is higher than that of the bottom topography. For smaller than this critical velocity, a stable quasi-linear solution which is similar to the linear solution exists. For larger than the critical velocity, three solutions whose form drag is very large exist which extend from the stable quasi-linear solution. It is inferred from the linear solution that these changes of the solution is due to the resonance of higher modes than that of the bottom topography. It is also found that the resonant velocity of the mode whose wavenumber is the same as the bottom topography has no e ect on these solutions. When the quiescent uid is accelerated by a constant wind stress, the acceleration stops around the critical velocity for wide range of the wind stress. If the wind stress is too large for the acceleration to stop there, the zonal current speed continues to increase in nitely. It is implied that the zonal velocity of equilibrium is mainly determined not by the wind stress but by the amplitude of the bottom topography and the viscosity coe cient. This implies that the zonal mean velocity does not change very much when the winds change.
Conffering University: 北海道大学
Degree Report Number: 甲第6986号
Degree Level: 博士
Degree Discipline: 地球環境科学
Type: theses (doctoral)
Appears in Collections:学位論文 (Theses) > 博士 (地球環境科学)

Submitter: 内本 圭亮

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