| YANG Bing,HOU Yijun. 2014. Near-inertial waves in the wake of 2011 Typhoon Nesat in the northern South China Sea. Acta Oceanologica Sinica, 33(11):102－111 |
| Near-inertial waves in the wake of 2011 Typhoon Nesat in the northern South China Sea |
| 南海北部2011年台风“纳沙”尾迹处近惯性内波特征的研究 |
| Received:December 26, 2013 Revised:May 22, 2014 |
| DOI：10.1007/s13131-014-0559-6 |
| Key words:near-inertial waves South China Sea Typhoon Nesat |
| 中文关键词: 近惯性内波 南中国海 台风“纳沙” |
| 基金项目: |
| Author Name | Affiliation | E-mail | | YANG Bing | Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
Key Laboratory of Chinese Academy of Sciences for Ocean Circulation and Waves, Institute of Oceanology, Qingdao 266071, China
University of Chinese Academy of Sciences, Beijing 100049, China | | | HOU Yijun | Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
Key Laboratory of Chinese Academy of Sciences for Ocean Circulation and Waves, Institute of Oceanology, Qingdao 266071, China | yjhou@qdio.ac.cn |
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| Abstract: |
| In September 2011, Typhoon Nesat passed over a moored array of instruments recording current and temperature in the northern South China Sea (SCS). A wake of baroclinic near-inertial waves (NIWs) commenced after Nesat passed the array. The associated near-inertial currents are surface-intensified and clockwise-polarized. The vertical range of NIWs reached 300 m, where the vertical range is defined as the maximum depth of the horizontal near-inertial velocity 5 cm/s. The current oscillations have a frequency of 0.709 9 cycles per day (cpd), which is 0.025f higher than the local inertial frequency. The NIWs have an e-folding time-scale of 10 d based on the evolution of the near-inertial kinetic energy. The depth-leading phase of near-inertial currents indicates downward group velocity and energy flux. The estimated vertical phase velocity and group velocity are 0.27 and 0.08 cm/s respectively, corresponding to a vertical wavelength of 329 m. A spectral analysis reveals that NIWs act as a crucial process to redistribute the energy injected by Typhoon Nesat. A normal mode and an empirical orthogonal function analysis indicate that the second mode has a dominant variance contribution of 81%, and the corresponding horizontal phase velocity and wavelength are 3.50 m/s and 420 km respectively. The remarkable large horizontal phase velocity is relevant to the rotation of the earth, and a quantitative analysis suggests that the phase velocity of the NIWs with a blue-shift of 0.025f overwhelms that of internal gravity waves by a factor of 4.6. |
| 中文摘要: |
| 2011年9月台风“纳沙”经过南中国海北部的锚定潜标, 该潜标观测到上层海洋的流速和温度响应。上层海洋的响应主要为台风尾迹处的斜压近惯性内波。近惯性流速呈现表层强化和顺时针极化的特征, 但是水深300m处近惯性流速依然达5cm/s。近惯性内波的频率为0.7099周每天, 比局地惯性频率高0.025f, 其中f为局地惯性频率。根据近惯性水平动能演化得到的近惯性内波e折时间为10天。近惯性流速的垂向分布呈现明显的位相上传, 表明下传的群速度和能量, 垂向相速度和群速度分别为0.27和0.08cm/s, 对应的垂向波长为329m。谱分析的结果表明在台风输入上混合层能量的再分配过程中近惯性内波起主要作用。垂向模态方程数值解和经验正交函数分解的结果表明近惯性内波以第二斜压模态为主(方差贡献81%), 其水平相速度和波长分别为3.50m/s和420km。由于地转的作用近惯性内波的水平相速度显著大于内重力波, 定量分析表明“蓝移”为0.025f的近惯性内波的相速度为相同层结下内重力波的4.6倍。 |
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