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Kelvin Waves around Antarctica

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  • 1 Institute of Low Temperature Science, Hokkaido University, Sapporo, Hokkaido, Japan
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Abstract

The Southern Ocean allows circumpolar structure and the Antarctic coastline plays a role as a waveguide for oceanic Kelvin waves. Under the cyclic conditions, the horizontal wavenumbers and frequencies for circumpolarly propagating waves are quantized, with horizontal wavenumbers 1, 2, and 3, corresponding to periods of about 32, 16, and 11 h, respectively. At these frequencies, westward-propagating signals are detected in sea level variation observed at Antarctic coastal stations. The occurrence frequency of westward-propagating signals far exceeds the statistical significance, and the phase speed of the observed signal agrees well with the theoretical phase speed of external Kelvin waves. Therefore, this study concludes that the observed, westward-propagating sea level variability is a signal of the external Kelvin waves of wavenumbers 1, 2, and 3 around Antarctica. A series of numerical model experiments confirms that Kelvin waves around Antarctica are driven by surface air pressure and that these waves are excited not only by local forcing over the Southern Ocean, but also by remote forcing over the Pacific Ocean. Sea level variations generated over the Pacific Ocean can travel to the western side of the South American coast and cross over Drake Passage to the Antarctic continent, constituting a part of the Kelvin waves around Antarctica.

Corresponding author address: Kazuya Kusahara, Institute of Low Temperature Science, Hokkaido University, N19W8, Kita-ku, Sapporo 060-0819, Japan. E-mail: kazuya.kusahara@lowtem.hokudai.ac.jp

Abstract

The Southern Ocean allows circumpolar structure and the Antarctic coastline plays a role as a waveguide for oceanic Kelvin waves. Under the cyclic conditions, the horizontal wavenumbers and frequencies for circumpolarly propagating waves are quantized, with horizontal wavenumbers 1, 2, and 3, corresponding to periods of about 32, 16, and 11 h, respectively. At these frequencies, westward-propagating signals are detected in sea level variation observed at Antarctic coastal stations. The occurrence frequency of westward-propagating signals far exceeds the statistical significance, and the phase speed of the observed signal agrees well with the theoretical phase speed of external Kelvin waves. Therefore, this study concludes that the observed, westward-propagating sea level variability is a signal of the external Kelvin waves of wavenumbers 1, 2, and 3 around Antarctica. A series of numerical model experiments confirms that Kelvin waves around Antarctica are driven by surface air pressure and that these waves are excited not only by local forcing over the Southern Ocean, but also by remote forcing over the Pacific Ocean. Sea level variations generated over the Pacific Ocean can travel to the western side of the South American coast and cross over Drake Passage to the Antarctic continent, constituting a part of the Kelvin waves around Antarctica.

Corresponding author address: Kazuya Kusahara, Institute of Low Temperature Science, Hokkaido University, N19W8, Kita-ku, Sapporo 060-0819, Japan. E-mail: kazuya.kusahara@lowtem.hokudai.ac.jp
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