Institutional Repository of Key Laboratory of Ocean Circulation and Wave Studies, Institute of Oceanology, Chinese Academy of Sciences
|Place of Conferral||中国科学院海洋研究所|
|Keyword||西北太平洋 近惯性振荡 潜标 着陆器|
对着陆器流场进行分析，发现南海具有强烈的半日分潮和全日分潮信号。此处的近惯性信号比潮汐信号小一个量级，但是存在一支传到600米水深以下的蓝移强近惯性振荡信号。该信号强度与潮信号同量级，持续时间从11月3日至16日。谱分析发现垂向流速呈现出五个不同的流核，最强流核发生在600米至650米位置。近惯性能量下传速度为67±5 m d-1，从600米下传到1000米的位置能量耗散18%。EOF分解结果显示，这次近惯性振荡信号开始是第一模态占主导，随后不稳定变成高阶模态。卫星的海表高度异常显示此时的正涡度有利于此次近惯性振荡发生蓝移。
Internal gravity waves are common phenomenon in the ocean. They occur in stratified waters, with the frequency in the range of f < σ < N, where f is the local Coriolis frequency and N is the buoyancy frequency. According to the characteristics and formation causes of the internal gravity wave, the wave is divided into internal tide (IT), near inertial wave (NIW) and solitary wave (SW). As the northwestern Pacific Ocean is high-incidence of the typhoon and mesoscale eddy, scientific research here is very important. However, due to the lack of observational data, the current mechanisms of transmission of NIWs, which are affected by water feature, are still poorly understood. The mooring data in the Northwest Pacific and the lander data in the northern part of the South China Sea were applied in this paper. Combined with the temperature data, salinity data by ARGO, the sea surface altimeter data by satellites and the typhoon meteorological data, the NIW signal influenced by one single typhoon and the multiple of five typhoons. The NIW signal in the deep water are analyzed in this research. The signal characteristics of NIW in the South China Sea and the Northwest Pacific Ocean are explained.
By analyzing the characteristics of the NIWs affecting the three typhoons in the western North Pacific, we find that the vertical group velocity of the three NIWs is smaller than that of the previous studies. Near inertial current has the characteristics of high vertical wavenumber. After theoretical analysis, we find that the high vertical wave number corresponds to a small vertical group velocity, which explains that the vertical group velocity is relatively small here. The three NIW signals are red-shifted. The red shift occurs in the first and second modes of EOF, and the third and fourth modes exhibit a blue-shifting. Since the NIW signals during non-typhoon are blue-shifted. Therefore, the typhoon can excite the NIW signal of the first two modes of EOF, and the near-inertial oscillation signal of the three-four mode is resonantly enhanced during the typhoon.
The analysis of the NIW signal under the influence of six typhoons in this area shows that when NIW signal is not exist, near-inertial oscillations were generated two days after the date during the typhoon was closest to of the mooring. But when NIW signal is exist, the new typhoon can enhance NIW before the closest date. Compared to the effect of a single typhoon, the energy can be transmitted to a deeper position after being affected by multiple typhoons.
Analysis of the lander flow field revealed that the South China Sea has a strong diurnal tide and semidiurnal tide signal. The near-inertial signal here is one order of magnitude smaller than the tidal signal, but there is a blue-shifted near-inertial oscillation signal that passes below 600 meters of water depth. The signal strength is of the same magnitude as the tidal signal and lasts from November 3 to 16. Spectral analysis revealed that the vertical flow rate exhibited five different current cores, with the strongest current cores occurring between 600 and 650 meters. The near-inertial energy transmission speed is 67±5 m d-1, and the energy dissipation from the 600-meter to the 1000-meter position is 18%. The EOF analysis results show that the NIW signal begins to dominate the first mode, and then becomes unstable to become a higher-order mode. Combined with the typhoon information, we found that the cause of the NIW signal was not caused by the typhoon. The sea surface height anomaly of the satellite data shows that the positive vorticity is favorable for the blue shift of the NIW during this time.
|MOST Discipline Catalogue||理学::海洋科学|
|Funding Project||National Natural Science Foundation of China|
|Table of Contents|
|侯华千. 西北太平洋近惯性振荡特征的研究[D]. 中国科学院海洋研究所. 中国科学院大学,2019.|
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