Collaborative Research: Breaking Wave Effects on Wave Boundary Layer and Air-Sea Momentum Flux

智力优势：海气通量参数化是海洋、大气和耦合海洋大气模式的重要组成部分。最近的飓风预测模式研究表明，在大风条件下，准确的通量参数化特别重要。然而，他们目前在运行模式中的海气通量参数化是基于简单的体积公式，显然远远不能令人满意。越来越多的观测证据表明，海气通量在很大程度上取决于海况。最近，首席研究员和他的同事们基于边界层能量和动量守恒的基本原理，开发了一种新的波边界层模型（大气边界层的下部，直接受表面波的影响）。该模型已与表面波模型相结合，用于预测成熟、生长和复杂海域的等效表面粗糙度和阻力系数。特别是，该模型预测，在飓风条件下，风速非常大时，阻力系数水平会降低，这与最近的现场和实验室观测结果一致。该模型的一个缺点是没有考虑表面破碎波对波浪边界层的影响。本文提出的波浪边界层和平衡波谱模型将基于以下假设：(1)破碎波在强风作用下显著改变了波浪边界层的结构和由此产生的海气动量通量。(2)在已知表面波谱和破碎波统计量的情况下，对现有的波浪边界层模式进行扩展，纳入破碎波峰的形式阻力效应和破碎波峰后气流分离效应（空间屏蔽效应），可以准确量化破碎波对海气动量通量的影响。(3)在平衡范围内，表面波谱和破碎波统计量也可以与海气动量通量一起预测。该模型将明确包括形式阻力和气流分离效应，并将用于预测大风条件下的阻力系数。接下来，该模型的每个组成部分将根据迈阿密大学的新实验室观测结果进行验证。该实验是专门为模型验证而设计的，并提供了总风应力、表面粘性应力、表面波谱和破碎波统计的同时测量。拟议的开发将与英国雷丁大学的斯蒂芬·贝尔彻密切合作。更广泛的影响:波浪边界层和平衡波谱的研究将是我们发展一套新的海气通量参数化的重要一步，该参数化将适用于整个风速范围和表面波条件，并可作为海洋、大气和海洋/大气耦合系统的高分辨率数值模式（包括热带气旋预测模式）的改进边界条件。因此，本研究解决了改善天气预报（特别是热带气旋预报）和减少极端风浪条件造成的自然灾害的社会需求。该项目包括开发一种新的实验技术来估计破碎波的统计量。海面破波事件的量化对海气相互作用研究的各个方面都非常重要。该项目还包括一名研究生的教育和培训。学生将学习实验室实验技术和理论/数值模拟方法来研究破碎波对海气相互作用过程的影响。最后，将促进现有的国际合作。

0526318Intellectual Merit: Air-sea flux parameterizations are important components of ocean, atmosphere, and coupled ocean atmosphere models. Accurate flux parameterizations are particularly important at high wind conditions as demonstrated by recent hurricane prediction model studies. Yet, ther present air-sea flux parameterizations in the operational models are based on simple bulk formulas and are clearly far from satisfactory. Increasing observational evidences suggest that air-sea fluxes strongly depend on sea states. Recently, the lead investigator and his colleagues have developed a new model of the wave boundary layer (the lower part of the atmospheric boundary layer that is directly influenced by surface waves) based on the fundamental principles of conservation of energy and momentum across the boundary layer. The model has been coupled with surface wave models to predict the equivalent surface roughness and the drag coefficient over mature, growing, and complex seas. In particular, the model predicts reduced levels of the drag coefficient at very high winds under hurricane conditions, consistent with recent field and laboratory observations. One shortcoming of the present model is that it does not include the effect of surface breaking waves on the wave boundary layer.The proposed model of the wave boundary layer and the equilibrium wave spectrum will be based on the following hypotheses: (1) Breaking waves significantly modify the structure of the wave boundary layer and the resulting air-sea momentum flux under strong wind forcing. (2) Breaking wave effects on the air-sea momentum flux can be quantified accurately if the existing wave boundary layer model is extended to incorporate the effect of the form drag due to breaking wave crests and the effect of airflow separation behind breaking wave crests that effectively shelters shorter waves from direct wind forcing (spatial sheltering effect), provided the surface wave spectrum and the breaking wave statistics are known. (3) In the equilibrium range, the surface wave spectrum and the breaking wave statistics may also be predicted together with the air-sea momentum flux. The model will explicitly include the form drag and airflow separation effects and will be used to predict the drag coefficient under high wind conditions. Next, each component of the model will be validated against new laboratory observations carried out at the University of Miami. The experiment is specifically designed for the model validation and provides simultaneous measurements of the total wind stress, the surface viscous stress, the surface wave spectrum, and the breaking wave statistics. The proposed development will be done in close collaboration with Stephen Belcher at the university of Reading, UK. Broader Impacts: The proposed study of the wave boundary layer and the equilibrium wave spectrum will be an important and essential step towards our ultimate goal of developing a new set of parameterizations of air-sea fluxes, which will be valid for the whole range of wind speeds and surface wave conditions and can be used as improved boundary conditions for high-resolution numerical models of ocean, atmosphere, and coupled ocean/atmosphere systems, including the tropical cyclone prediction models. Therefore, this research addresses social needs to improve weather forecast (in particular, tropical cyclone forecast) and to reduce natural hazards caused by extreme wind and wave conditions. The project includes the development of a new experimental technique to estimate the breaking wave statistics. Quantifying surface breaking wave events is extremely important for all aspects of the air-sea interaction studies. The project also involves the education and training of one graduate student. The student will learn both laboratory experimental techniques and theoretical/numerical modeling approaches to study breaking wave effects on air-sea interaction processes. Finally, an existing international collaboration will be fostered.