Poleward-propagating near-inertial waves enabled by the western boundary current

Chanhyung Jeon, Jae Hun Park, Hirohiko Nakamura, Ayako Nishina, Xiao Hua Zhu, Dong Guk Kim, Hong Sik Min, Sok Kuh Kang, Hanna Na, Naoki Hirose

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Abstract

Near-inertial waves (NIWs), which have clockwise (anticlockwise) rotational motion in the Northern (Southern) Hemisphere, exist everywhere in the ocean except at the equator; their frequencies are largely determined by the local inertial frequency, f. It is thought that they supply about 25% of the energy for global ocean mixing through turbulence resulting from their strong current shear and breaking; this contributes mainly to upper-ocean mixing which is related to air-sea interaction, typhoon genesis, marine ecosystem, carbon cycle, and climate change. Observations and numerical simulations have shown that the low-mode NIWs can travel many hundreds of kilometres from a source region toward the equator because the lower inertial frequency at lower latitudes allows their free propagation. Here, using observations and a numerical simulation, we demonstrate poleward propagation of typhoon-induced NIWs by a western boundary current, the Kuroshio. Negative relative vorticity, meaning anticyclonic rotational tendency opposite to the Earth’s spin, existing along the right-hand side of the Kuroshio path, makes the local inertial frequency shift to a lower value, thereby trapping the waves. This negative vorticity region works like a waveguide for NIW propagation, and the strong Kuroshio current advects the waves poleward with a speed ~85% of the local current. This finding emphasizes that background currents such as the Kuroshio and the Gulf Stream play a significant role in redistribution of the NIW energy available for global ocean mixing.

Original languageEnglish
Article number9955
JournalScientific reports
Volume9
Issue number1
DOIs
Publication statusPublished - Dec 1 2019

All Science Journal Classification (ASJC) codes

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    Jeon, C., Park, J. H., Nakamura, H., Nishina, A., Zhu, X. H., Kim, D. G., Min, H. S., Kang, S. K., Na, H., & Hirose, N. (2019). Poleward-propagating near-inertial waves enabled by the western boundary current. Scientific reports, 9(1), [9955]. https://doi.org/10.1038/s41598-019-46364-9