Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, 266071, China.
University of Chinese Academy of Sciences, Beijing, China.
Sci Rep. 2019 Dec 31;9(1):20417. doi: 10.1038/s41598-019-56822-z.
Near-inertial waves (NIWs) contain a pronounced portion of shear energy in the internal wave field and is of great importance to deep ocean mixing. However, accurate simulation of NIWs remains a challenge. Here we analyzed 3-year long mooring observation of velocity profiles over 80-800 m to study the responses of near-inertial downward shear to varying wind stress curls and sea level anomalies (SLAs). It is demonstrated that moderate (even weak) cyclone makes more contributions to enhanced shear below the pycnocline than very strong cyclone. Because very strong curl can stall the downward propagation of large shear. The large positive and negative SLAs cause the accumulation of large shear in the lower and upper parts of the pycnocline through inducing downwelling and upwelling motions, respectively. Time variation of near-inertial shear was strongly influenced by cases of large curls and interannual variation of SLA, and thus did not follow the seasonal variation of wind stress. Our analyses suggest that matched fields of wind stress curl and SLA, and well representing the ocean response to moderate cyclone are needed in simulating the role of NIWs on mixing.
近惯性波（NIWs）在内部波场中包含显著的剪切能量部分，对深海混合具有重要意义。然而，NIWs 的准确模拟仍然是一个挑战。在这里，我们分析了长达 3 年的在 80-800 米深度的锚定观测速度剖面，以研究近惯性向下剪切对变化的风应力卷曲和海平面异常（SLAs）的响应。结果表明，中等（甚至弱）气旋比非常强的气旋对密度跃层以下的剪切增强贡献更大。因为非常强的卷曲会阻碍大剪切的向下传播。大的正、负海平面异常通过诱导下沉和上升运动，分别导致密度跃层上下部分的大剪切积累。近惯性剪切的时间变化受到大卷曲和 SLA 的年际变化的强烈影响，因此不遵循风应力的季节性变化。我们的分析表明，在模拟 NIWs 对混合的作用时，需要匹配风应力卷曲和 SLA 的场，并很好地表示海洋对中等气旋的响应。
