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Generation and Growth Mechanism of the Natal Pulse

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  • 1 Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
  • | 2 Atmosphere and Ocean Research Institute, University of Tokyo, Chiba, Japan
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Abstract

The Natal pulses, solitary cyclonic meanders in the Agulhas Current, are reproduced in an ocean general circulation model. The model covers the region around the Agulhas Current with a grid fine enough to reproduce major eddies. The features of the reproduced Natal pulses are consistent with observational evidences in the following respects: they are generated at the Natal Bight when anticyclonic eddies come, move downstream along the Agulhas Current at speeds about 20 km day−1, and grow in its horizontal size as they move. The present simulation shows that the generation and growth of the Natal pulse occurs because of the interaction between the mean flow of the Agulhas Current and an anticyclonic eddy. A supplemental simulation, where the topography of the Natal Bight is modified, indicates that the topography of the Natal Bight does not cause the generation of the Natal pulses, contrary to a previous suggestion.

Corresponding author address: Motohiko Tsugawa, 3173-25, Showa-machi, Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan. Email: tsugawa@jamstec.go.jp

Abstract

The Natal pulses, solitary cyclonic meanders in the Agulhas Current, are reproduced in an ocean general circulation model. The model covers the region around the Agulhas Current with a grid fine enough to reproduce major eddies. The features of the reproduced Natal pulses are consistent with observational evidences in the following respects: they are generated at the Natal Bight when anticyclonic eddies come, move downstream along the Agulhas Current at speeds about 20 km day−1, and grow in its horizontal size as they move. The present simulation shows that the generation and growth of the Natal pulse occurs because of the interaction between the mean flow of the Agulhas Current and an anticyclonic eddy. A supplemental simulation, where the topography of the Natal Bight is modified, indicates that the topography of the Natal Bight does not cause the generation of the Natal pulses, contrary to a previous suggestion.

Corresponding author address: Motohiko Tsugawa, 3173-25, Showa-machi, Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan. Email: tsugawa@jamstec.go.jp

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