Spectral Energy Dissipation in Broad-banded Wave Fields

在之前由美国国家科学基金会资助的一项研究中，该团队在远程估计公海海浪破碎的能量耗散方面取得了重大进展，在该研究中，他们验证了在没有涌浪的情况下对风浪破碎的远程观测。该项目将把这项研究扩展到宽带波场(即混合海洋)。具体目标是：1.利用宽带波场中的同步现场观测验证Phillips(1985)分布的能量耗散；2.确定能量耗散与波龄和频率方向传播的关系；3.确定能量耗散与波龄和频率方向传播的关系。验证一种常用的平衡近似的有效性，在平衡近似中，能量耗散由风输入来平衡。将进行两个现场实验，通过同步的远程和现场观测来估计波浪破碎时的能量耗散。这些实验将从最近在华盛顿湖和普吉特海湾观察到的窄带破碎波中的能量耗散逐步扩展(汤姆森等人，2009年)。第一次实验将在胡安德富卡海峡进行，第二次实验将在北太平洋进行。一种基于傅立叶的方法(Thomson和Jessup，2009)在窄带波的远程观测中表现良好，但它将适用于宽带波。一种结构函数方法(Gemmrich，2009)用于现场速度的平稳多普勒剖面，将适用于一个新的自由漂移平台的观测。波浪破碎过程中能量耗散的智能价值量化对于准确模拟波浪和海况的演变至关重要。这项拟议的研究将继续测试和应用一种假设，即使用波峰分布来远程估计耗散[Phillips，1985]。远程估计是频谱的，因此是数值模式的理想输入，然而，估计需要确定无标度破缺参数b。Phillips公式最近得到了验证，包括确定了窄带波场的b(Thomson等人，2009年)，但不适用于典型的开阔海洋条件下的宽带波场。拟议的研究将扩大验证范围，同时评估断路与频率方向传播、波浪年龄和风应力的相关性。布罗德影响拟议的研究将包括培训一名博士生，该博士生将参与工作的所有方面。拟议的研究将被纳入正在进行的外联活动，包括在华盛顿周末(华盛顿大学开放参观)期间的示威活动，以及在KCTS公共电视台？S科学咖啡馆的演讲。拟议研究的结果将在会议上和同行评议的期刊上公布。结果的潜在应用包括改进的全球海浪模型，用于气候预测和航运/海军行动。

This team has made significant progress toward remotely estimating energy dissipation by wave breaking in the open ocean in a previous NSF-funded study in which they validated remote observations of wind-wave breaking in the absence of swell. This project will extend that research to broad-banded wave fields (i.e., mixed seas). The specific objectives are to:1. Validate energy dissipation from the Phillips (1985) distribution using simultaneous in situ observations in broad-banded wave fields,2. Determine the dependence of energy dissipation on wave age and frequency-directional spread, and3. Test the validity of a commonly used equilibrium approximation, in which energy dissipation is balanced by wind input.Two field experiments will be conducted to estimate energy dissipation during wave breaking via simultaneous remote and in situ observations. The experiments will extend incrementally from recent observations of energy dissipation in narrow-banded breaking waves on Lake Washington and Puget Sound (Thomson et al., 2009). The first experiment will be in the Juan de Fuca Strait, and the second experiment will be in the North Pacific. A Fourier based method (Thomson and Jessup, 2009) that has performed well for remote observations of narrow-banded waves will be adapted to broad-banded waves. A structure function method (Gemmrich, 2009) developed for stationary Doppler profiles of in situ velocity will be adapted to observations from a new free drifting platform.Intellectual MeritQuantification of energy dissipation during wave breaking is essential for accurate modeling of waves and the evolution of sea states. The proposed research will continue testing and application of a hypothesis for remotely estimating dissipation using the distribution of wave crests [Phillips, 1985]. The remote estimates are spectral, and thus ideal as input to numerical models, however the estimates require determination of a scale-free breaking parameter b. The Phillips formulation recently has been validated, including determination of b, for narrow-banded wave fields (Thomson et al., 2009), but not for the broad-banded wave fields that are typical of open ocean conditions. The proposed research will expand the validation, while evaluating the dependence of breaking on frequency-directional spreading, wave age, and wind stress.Broader ImpactsThe proposed research will include training of a PhD student, who will participate in all aspects of the work. The proposed research will be incorporated into ongoing outreach activities, including demonstrations during Washington Weekend (University of Washington open house) and presentations at KCTS public television?s Science Café. Results from the proposed research will be presented at conferences and in peer-reviewed journals. Potential applications of the results include improved global wave models for climate predictions and shipping/naval operations.