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SUN Zhenyu,HU Jianyu,ZHENG Quanan,GAN Jianping. 2015. Comparison of typhoon-induced near-inertial oscillations in shear flow in the northern South China Sea. Acta Oceanologica Sinica, 34(11):38-45
Comparison of typhoon-induced near-inertial oscillations in shear flow in the northern South China Sea
南海北部流切变环境中台风引起的近惯性振荡的比较研究
Received:March 19, 2015  Revised:July 02, 2015
DOI:10.1007/s13131-015-0746-0
Key words:near-inertial oscillation  typhoon  northern South China Sea
中文关键词:  近惯性振荡  台风  南海北部
基金项目:The National Basic Research Program (973 Program) of China under contract Nos 2015CB954004 and 2009CB421208; the National Natural Science Foundation of China under contract Nos 41276006U1405233 and 40976013; the Open Fund of the Key Laboratory of Ocean Circulation and Waves, Chinese Academy of Sciences under contract No. KLOCAW1307.
Author NameAffiliationE-mail
SUN Zhenyu State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361102, China sunzy@xmu.edu.cn 
HU Jianyu State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361102, China  
ZHENG Quanan Department of Atmospheric and Oceanic Science, University of Maryland, College Park, Maryland 20742, USA  
GAN Jianping Department of Mathematics and Division of Environment, Hong Kong University of Science and Technology, Kowloon, Hong Kong, China  
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Abstract:
      With moorings equipped with Acoustic Doppler Current Profilers (ADCP) in the northern South China Sea (SCS) in 2008 and 2009, we observed three near-inertial oscillation (NIO) events coded 2008a, 2009a and 2009b induced by passages of typhoons or tropical storms. This study compares characteristics of the three NIO events. Event 2008a was the strongest one among the three, and had the longest sustaining period (15 d), while events 2009a and 2009b sustained for only 4 and 8 d, respectively. The three events were distinguished by vertical energy distribution and phase propagation. As for the frequency shift of the NIO, event 2008a had a peak frequency lower than the local Coriolis frequency (red-shift), while events 2009a and 2009b showed blue-shift. The behavior of individual NIO event is jointly decided by the typhoon disturbance and the background ocean condition. Especially the background flow plays an important role by effects of advection and modulation. The results in this study provide observational evidence of variational NIO response to background flow field. As indicated by the distribution of vorticity and effective Coriolis frequency derived from numerical modeling, the large amplitude and elongated sustaining period of event 2008a were attributed to the waveguide effect of the background shear flow. This effect redistributed the NIO energy after the typhoon passage, absorbed incident waves and trapped energy in the area of the negative vorticity. While the background flow during events 2009a and 2009b did not have such effects due to the near-zero vorticity in the mooring area.
中文摘要:
      通过2008年和2009年布放在南海北部的声学多普勒流速剖面仪(ADCP)锚系潜标,本文观测到了三次由台风引起的近惯性振荡(NIO)事件,分别编号为2008a,2009a,2009b,并对其进行了比较研究.其中2008a在三次事件中强度最大,持续时间最长(15 d),而2009a和2009b仅分别持续了4 d和8 d.三次事件的垂直能量分布和位相传播有明显的区别.在频率偏移方面,2008a的峰值频率略低于局地科氏频率(红移),而2009a和2009b则体现出蓝移.不同的NIO事件的特征表现主要由台风扰动和背景流场环境共同决定,特别是背景流场通过平流和调制作用在其中起了重要的作用.本文的研究为不同背景流场中NIO的不同响应提供了观测的证据.通过分析数模提供的背景流场的涡度和有效科氏频率,2008a事件中较强的振幅和较长的持续时间是由于背景的剪切流场的波导效应造成,其改变了台风过后NIO的能量分布,将入射波能量集中于负涡度区域.而2009a和2009b事件中由于涡度不明显,因此没有类似效应.
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