Driving Mechanism of Band Structure of Mean Current over the Continental Shelf

Atsuhiko Isobe Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka, Japan

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Abstract

A two-layer numerical model is used to investigate the continental-shelf circulation forced by western boundary currents along shelf edges. Emphasis is placed on an effect by frontal eddies (or frontal waves), which are reproduced in the model with the shelf edge along which a western boundary current is imposed. 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 generation of the band structure is consistent with the observational results obtained by acoustic Doppler current profilers on the shelf of the East China Sea. The western boundary current is accompanied by frontal waves, and so vertical momentum transfer occurs because of 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.

Corresponding author address: Dr. Atsuhiko Isobe, Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1, Kasuga-Koen, Kasuga, Fukuoka 816-8580, Japan. Email: isobe@esst.kyushu-u.ac.jp

Abstract

A two-layer numerical model is used to investigate the continental-shelf circulation forced by western boundary currents along shelf edges. Emphasis is placed on an effect by frontal eddies (or frontal waves), which are reproduced in the model with the shelf edge along which a western boundary current is imposed. 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 generation of the band structure is consistent with the observational results obtained by acoustic Doppler current profilers on the shelf of the East China Sea. The western boundary current is accompanied by frontal waves, and so vertical momentum transfer occurs because of 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.

Corresponding author address: Dr. Atsuhiko Isobe, Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1, Kasuga-Koen, Kasuga, Fukuoka 816-8580, Japan. Email: isobe@esst.kyushu-u.ac.jp

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