Poleward-propagating near-inertial waves enabled by the western boundary current
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. NPG Scientific Reports 9(1): 7 pp. https://dx.doi.org/10.1038/s41598-019-46364-9
In: Scientific Reports (Nature Publishing Group). Nature Publishing Group: London. ISSN 2045-2322; e-ISSN 2045-2322, more
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| Authors | | Top |
- Jeon, C.
- Park, J.-H.
- Nakamura, H.
- Nishina, A.
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- Zhu, X.-H.
- Kim, D.G.
- Min, H.S.
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- Kang, S.K.
- Na, H.
- Hirose, N.
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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. |
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