Statistical and dynamical analyses of generation mechanisms of solitary internal waves in the northern South China Sea
Statistical and dynamical analyses of generation mechanisms of solitary internal waves in the northern South China Sea
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DOI：
10.1029/2006jc003551
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发表时间：
2007-03
影响因子：
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通讯作者：
Q. Zheng;R. Susanto;Chung‐Ru Ho;Y. Song;Qing Xu
中科院分区：
文献类型：
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作者：
Q. Zheng;R. Susanto;Chung‐Ru Ho;Y. Song;Qing Xu
[1]分析了温跃层浅化对南海北部中国海区海洋内波产生的影响。利用1995~2001年7年的卫星合成孔径雷达(SAR)图像，统计分析了IW的发生情况，并利用海面风、海况和垂直温度廓线的实测资料，分析了IW的产生和SAR成像条件。IW包的纬度分布表明，分布在118°E以东的IW包中有22%明显起源于吕宋海峡，而118°E以西的IW包中有78%可能是从东方传播或演化为起源于东界的孤子，这是由于浅海温跃层的裂变效应所致。IW发生频数的年际分布具有年际变异性，表明存在长期的大尺度过程对SAR观测到的IW发生进行修正。从SAR观测的月平均IW出现频率来看，高频分布在4~7月，6月份达到峰值，最大出现频率为20%。低发生频率分布在冬季12月至次年2月，2月最低为1.5%。这项研究提出了IW产生需要的充要条件：初始扰动形成和波幅增长。由于初始扰动的耗散效应，只有完全长大的波才有机会辐射出震源区。采用物理模型和pkdV方程分析了孤立波幅度增长的充分条件。结果表明，温跃层浅化对孤子振幅增长具有强迫作用，因此孤子振幅增长率(SAGR)是IW出现频率的决定性因素。理论分析预测两者之间存在线性关系。将理论模型应用于吕宋海峡的实地测量，3-11月的相关系数高达0.845，置信度为99%。线性回归给出了IW发生的相关系数(R2)为0.6519，SAGR阈值(最小值)为0.9。根据理论解，向东传播的扰动没有机会发展，因此它们几乎不会出现在吕宋海峡东部海脊的东侧。
[1] This study analyzes the effects of thermocline shoaling on the ocean internal wave (IW) generation in the north South China Sea (NSCS). Seven years of satellite synthetic aperture radar (SAR) images from 1995 to 2001 are used for the statistical analysis of IW occurrence, and field measurements of sea surface wind, sea state, and vertical temperature profiles are used for analyzing IW generation and SAR imaging conditions. Latitudinal distribution of IW packets shows that 22% of IW packets distributed in the east of 118°E obviously originate from the Luzon Strait, and 78% of IW packets west of 118°E may propagate from the east or evolve into the solitons originating from the east boundary owing to the fission effect of shoaling thermocline. The yearly distribution of IW occurrence frequencies reveals an interannual variability, implying that there are long-term and large-scale processes modifying the SAR-observed IW occurrence. The monthly SAR-observed IW occurrence frequencies show that the high frequencies are distributed from April to July and reach a peak in June with a maximum frequency of 20%. The low occurrence frequencies are distributed in winter from December to February of next year with a minimum frequency of 1.5% in February. This study proposes that the IW generation needs the necessary and sufficient conditions: initial disturbance formation and wave amplitude growth. Owing to the dissipation effect on the initial disturbance, only fully grown waves have a chance to radiate out of the source region. A physical model and PKdV equation are adopted for analyzing the sufficient conditions for solitary IW amplitude growth. The results indicate that the thermocline shoaling provides the forcing to soliton amplitude growth, so that the soliton amplitude growth ratio (SAGR) serves as a decisive factor for the IW occurrence frequency. Theoretical analysis predicts a linear relation between the two. Application of theoretical models to field measurements in the Luzon Strait gives a correlation coefficient as high as 0.845 with a confidence level of 99% for months from March to November. The linear regression gives a correlation coefficient (R2) of 0.6519 and a SAGR threshold (minimum) value of 0.90 for IW occurrence. According to the theoretical solutions, the eastward propagating disturbances have no chance to grow up, so that they hardly appear on the east side of the submarine ridges in the eastern Luzon Strait.