Observation of Near-Inertial Oscillations Induced by Energy Transformation during Typhoons

Huaqian Hou, Fei Yu, Feng Nan, Bing Yang, Shoude Guan and Yuanzhi Zhang
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Huaqian Hou: Key Laboratory of Ocean Circulation and Wave Studies, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
Fei Yu: Key Laboratory of Ocean Circulation and Wave Studies, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
Feng Nan: Key Laboratory of Ocean Circulation and Wave Studies, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
Bing Yang: Key Laboratory of Ocean Circulation and Wave Studies, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
Shoude Guan: Key Laboratory of Ocean Circulation and Wave Studies, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
Yuanzhi Zhang: Nanjing University of Information Science and Technology, Nanjing 210044, China

Energies, 2018, vol. 12, issue 1, 1-19

Abstract: Three typhoon events were selected to examine the impact of energy transformation on near-inertial oscillations (NIOs) using observations from a subsurface mooring, which was deployed at 125° E and 18° N on 26 September 2014 and recovered on 11 January 2016. Almost 16 months of continuous observations were undertaken, and three energetic NIO events were recorded, all generated by passing typhoons. The peak frequencies of these NIOs, 0.91 times of the local inertial frequency f , were all lower than the local inertial frequency f . The estimated vertical group velocities ( C gz ) of the three NIO events were 11.9, 7.4, and 23.0 m d −1 , and were relatively small compared with observations from other oceans (i.e., 100 m d −1 ). The directions of the horizontal near-inertial currents changed four or five times between the depths of 40 and 800 m in all three NIO events, implying that typhoons in the northwest Pacific usually generate high-mode NIOs. The NIO currents were further decomposed by performing an empirical orthogonal function (EOF) analysis. The first and second EOF modes dominated the NIOs during each typhoon, accounting for more than 50% of the total variance. The peak frequencies of the first two EOF modes were less than f , but those of the third and fourth modes were higher than f . The frequencies of all the modes during non-typhoon periods were more than f . Our analysis indicates that the relatively small downward group velocity was caused by the frequent direction changes of the near-inertial currents with depth.

Keywords: Near-inertial kinetic energy; vertical group velocity; near-inertial oscillations; energy transformation (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2018
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