| CHEN Shengli,HU Jianyu,POLTON Jeff A.. 2015. Features of near-inertial motions observed on the northern South China Sea shelf during the passage of two typhoons. Acta Oceanologica Sinica, 34(1):38－43 |
| Features of near-inertial motions observed on the northern South China Sea shelf during the passage of two typhoons |
| 南海北部陆架区两个台风过境时近惯性运动的若干特征 |
| Received:April 08, 2014 Revised:June 13, 2014 |
| DOI：10.1007/s13131-015-0594-y |
| Key words:near-inertial motions typhoon South China Sea |
| 中文关键词: 近惯性运动 台风 南海 |
| 基金项目:The National Natural Science Foundation of China under contract Nos 41276006, 40976013 and 41121091; the China Scholarship Council; the UK Natural Environment Research Council Programme FASTNEt under contract No. NE/I030259/1. |
| Author Name | Affiliation | E-mail | | CHEN Shengli | State Key Laboratory of Marine Environmental Science, College of Ocean & Earth Sciences, Xiamen University, Xiamen 361102, China
National Oceanography Centre, Liverpool L3 5dA, UK | | | HU Jianyu | State Key Laboratory of Marine Environmental Science, College of Ocean & Earth Sciences, Xiamen University, Xiamen 361102, China | hujy@xmu.edu.cn | | POLTON Jeff A. | National Oceanography Centre, Liverpool L3 5dA, UK | |
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| Abstract: |
| Features of near-inertial motions on the shelf (60 m deep) of the northern South China Sea were observed under the passage of two typhoons during the summer of 2009. There are two peaks in spectra at both sub-inertial and super-inertial frequencies. The super-inertial energy maximizes near the surface, while the sub-inertial energy maximizes at a deeper layer of 15 m. The sub-inertial shift of frequency is induced by the negative background vorticity. The super-inertial shift is probably attributed to the near-inertial wave propagating from higher latitudes. The near-inertial currents exhibit a two-layer pattern being separated at mid-depth (25-30 m), with the phase in the upper layer being nearly opposite to that in the lower layer. The vertical propagation of phase implies that the near-inertial energy is not dominantly downward. The upward flux of the near-inertial energy is more evident at the surface layer (<17 m). There exist two boundaries at 17 and 40 m, where the near-inertial energy is reflected upward and downward. The near-inertial motion is intermittent and can reach a peak of as much as 30 cm/s. The passage of Typhoon Nangka generates an intensive near-inertial event, but Typhoon Linfa does not. This difference is attributed to the relative mooring locations, which is on the right hand side of Nangka's path (leading to a wind pattern rotating clockwise with time) and is on the left hand side of Linfa's path (leading to a wind pattern rotating anti-clockwise with time). |
| 中文摘要: |
| 利用2009年夏季在南海北部陆架区(水深60米)两个台风过境时的锚系资料, 发现了近惯性运动的若干新特征. 频谱分析表明, 在略低于惯性频率(红移)和略高于惯性频率(蓝移)处, 同时存在明显的谱峰. 蓝移能量的垂直结构是典型的表层最大, 而红移能量的最大值却发生在15米的次表层. 频率的红移是背景负涡度引起的, 蓝移的发生很可能是源于从纬度更高海区传播而来的近惯性波. 近惯性流呈现双层结构, 以中间水深(25-30米)为界, 上层的相位与下层的几乎相反. 相位的垂直传递表明, 近惯性能量的下传并不占主导优势, 在表层(<17米)近惯性能量的上传更为明显. 水深17米和40米似乎是两个边界, 此处近惯性能量发生向上和向下反射. 近惯性运动的强度随时间变化, 最大值达到30厘米每秒, 它与台风过境引起的风场变化密切相关. 当台风"浪卡"过境时生成较强的近惯性运动, 而台风"莲花"过境时却没有. 这是因为锚系位于"浪卡"前进路径的右侧, 导致锚系位置的风应力随时间顺时针旋转, 而台风"莲花"过境时, 锚系位于台风前进路径的左侧, 该点的风应力随时间逆时针旋转. |
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