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 similar to 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.
1.Inha Univ, Dept Marine Sci & Biol Engn, Incheon, South Korea 2.Inha Univ, Dept Ocean Sci, Incheon, South Korea 3.Kagoshima Univ, Fac Fisheries, Kagoshima, Japan 4.Minist Nat Resources, State Key Lab Satellite Ocean Environm Dynam, Inst Oceanog 2, Hangzhou, Zhejiang, Peoples R China 5.Southern Marine Sci & Engn Guangdong Lab Zhuhai, Zhuhai, Peoples R China 6.Korea Inst Ocean Sci & Technol, Busan, South Korea 7.Seoul Natl Univ, Seoul, South Korea 8.Kyushu Univ, Res Inst Appl Mech, Kasuga, Fukuoka, Japan
Recommended Citation:
Jeon, Chanhyung,Park, Jae-Hun,Nakamura, Hirohiko,et al. Poleward-propagating near-inertial waves enabled by the western boundary current[J]. SCIENTIFIC REPORTS,2019-01-01,9