Impact of swell on the wind-sea and resulting modulation of stress
Impact of swell on the wind-sea and resulting modulation of stress
复制标题
涌浪对风海的影响以及由此产生的应力调制
DOI：
10.1016/j.pocean.2019.102164
复制
发表时间：
2019
影响因子：
4.1
通讯作者：
Collins, Clarence O.
中科院分区：
文献类型：
--
作者：
Vincent, Charles L.;Thomson, Jim;Graber, Hans C.;Collins, Clarence O.
来自太平洋、大西洋和墨西哥湾的37，106个海洋表面波谱的研究表明，涌浪调制风-海浪波谱的高频尾部的能量水平，改变海面粗糙度。在海浪和涌浪混合的情况下，谱的风-海部分遵循众所周知的f-4（平衡范围）和f-5（饱和范围）幂律。膨胀调节能级，但不改变幂律结构。对于具有最小风速的涌浪，谱遵循− 4、− 5幂律范例，但能量与涌浪陡度相关，而不是风速。膨胀使两个子范围之间的过渡向较低频率偏移。对于涌浪混合物，提出了一个调制因子λ，它取决于风速和涌浪陡度，允许谱尾参数化。将大涌浪和小风的谱与相同高度和周期的风-海谱进行比较，发现谱的形状差别不大，说明Hasselmann Snl源项可能是能量转移到风-海尾引起调制的机制。对Papa海洋站的33，000多个方向谱的分析表明，风-海高频尾部的平均方向与风向密切相关，无论涌浪方向或陡度或涌浪优势水平如何。本文导出了有涌浪时的摩擦流速（u* s）方程：u * s= λ 1/2 u * o其中u * o是无涌浪时的摩擦流速，忽略了涌浪的直接影响。注意，这只是总测量应力的部分估计，对3，000+个观测光谱的预测进行评估，产生0.91的相关性，表明它可能是重要的。u/u o的观测结果表明，与膨胀陡度的相关性与λ 1/2预测的相似。在低风速下，λ 1/2高估了应力，但注意，它是在没有来自涌浪频率的分量的情况下得出的。在尾部，动量传输是向下的，而在涌浪中，动量传输主要是向上的，这表明可能对λ 1/2进行了修正。讨论了涌浪产生的风的情况。
Investigation of 37,106 ocean surface wave spectra from the Pacific, Atlantic Ocean, and Gulf of Mexico demonstrate that swell modulates the energy level of the high frequency tail of the wind-sea wave spectrum, altering sea surface roughness. With a mixture of sea and swell, the wind-sea part of spectra follows the well-known f-4 (equilibrium range) and f-5 (saturation range) power laws. Swell modulates the energy levels but does not change the power-law structure. For swell with minimal winds, the spectra follow the− 4,− 5 power-law paradigm, but energy correlates to swell steepness not wind speed. Swell shifts the transition between the two sub-ranges towards lower frequencies. For sea-swell mixtures, a modulation factor λ is proposed that depends on wind speed and swell steepness which allows parameterization of the spectral tail. Comparison of large swell with little wind to wind-sea spectra of same height and period, indicates that there is little difference in spectral shape and suggests that the Hasselmann S nl source term is likely the mechanism by which energy is transferred into the wind-sea tail causing the modulation. Analysis of 33,000+ directional spectra at Ocean Station Papa shows that the mean direction for the wind-sea high frequency tail is strongly correlated to wind direction, no matter the swell direction or steepness or level of swell dominance. An equation for the friction velocity of a sea state with swell (u* s) is developed, u∗ s= λ 1/2 u∗ o where u∗ o is the friction velocity in the absence of swell, by neglect of the direct swell impact. Noting that this is only a partial estimate of the total measured stress, the prediction is evaluated for 3,000+ observed spectra yielding a correlation of 0.91 suggesting that it may be of consequence. Observations of u∗/u∗ o suggest a dependence with swell steepness that is similar to that predicted by λ 1/2. At low winds, λ 1/2 overestimates the stress, but noting that it was derived absent the components from the swell frequencies. In the tail, the momentum transport is downward, while in the swell the transport is predominantly upward, suggests a possible correction for λ 1/2. The case of a swell generated wind is discussed.
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