Impact of Surface Wave Dependent Air-Sea Fluxes on Tropical Cyclone Prediction

智力优势：目前在大多数飓风研究和预报模式中使用的大量海气动量通量参数化是基于在风力弱得多的地区进行的现场测量的外推。这些参数化预测了交换系数随风速的单调增加。然而，最近的观测、理论和实验结果表明，在大风条件下，海气动量通量强烈地依赖于波场，并且阻力系数在非常高的风速下停止增加，甚至可能减少。这些因素可能导致目前的模式大大低估了地面风。最近，首席研究员（pi）开发了一种耦合波风（CWW）模型，该模型提供了与最近观测一致的地表动量通量。该模型明确地计算了任何给定波场的波浪诱发应力和由此产生的阻力系数，即使是在飓风驱动的复杂海域。CWW模式的数值实验清楚地表明，高风速下的动量通量与弱风速下的动量通量完全不同，并且由于海浪的影响，动量通量随与风暴中心的相对位置而有明显的变化。这些结果强烈表明，飓风条件下动量通量的适当估计只能通过将海浪模式和波浪边界模式合并到飓风-海洋模式中来实现。假设：(1)飓风条件下的地表动量通量强烈依赖于海浪场的时空变化。在飓风条件下，破浪的影响是显著的。利用CWW模式可以准确预测飓风条件下的动量通量。(2)海气动量通量的参数化对飓风强度和最大风速预报有显著影响。特别是，阻力系数的时空变异性对预测有重大影响。因此，将CWW模式与飓风-海洋预报模式耦合，将系统地提高对飓风强度和风结构的预报能力。为了验证这些假设，pi将执行四项具体任务：(1)将破碎波效应纳入CWW模型；(2)将CWW模型与罗德岛大学地球物理流体动力学实验室/飓风海洋模型相结合，建立风浪-海洋耦合飓风预测模型；(3)研究新的通量参数化如何影响理想化和实际热带风暴的飓风强度、路径和风结构预测。(4)与参与海军研究办公室赞助的耦合边界层/海气转移（CBLAST）计划和韩国海洋研究开发研究所（KORDI）的科学家合作，将模型结果与现有和新获得的实验数据进行比较。更广泛的影响：这项研究解决了更好地预测和减轻由飓风产生的极端风、浪和雨造成的自然灾害的社会需求。该项目涉及一名研究生和博士后科学家的教育和培训。这项工作通过利用KORDI的飓风观测塔数据促进国际合作，并为KORDI提供新的海气模拟技术。通过与KORDI的合作，该塔的数据将用于研究高风速下的海气通量及其对热带气旋预测的影响。

Intellectual Merit: Present bulk parameterizations of air-sea momentum fluxes used in most hurricane research and forecast models are based on extrapolation from field measurements in much weaker wind regimes. These parameterizations predict monotonic increases of the exchange coefficients with wind speed. However, recent observational, theoretical, and experimental results demonstrate that air-sea momentum flux at high wind conditions strongly depends on the wave field and that the drag coefficient ceases to increase and may even decrease at very high wind speeds. These factors may cause current models to significantly underestimate surface winds.Recently, the Principal Investigators (PIs) have developed a coupled wave-wind (CWW) model, which provides surface momentum fluxes that are consistent with recent observations. The model explicitly calculates the wave-induced stress and resulting drag coefficient for any given wave field, even for complex seas driven by hurricanes. Numerical experiments using the CWW model clearly indicate that the behavior of momentum flux at high wind speeds is completely different from that at weak wind speeds and that the momentum flux varies significantly depending on the relative position from the storm center due to influence of ocean waves. These results strongly suggest that proper estimation of momentum flux in hurricane conditions can be only achieved by incorporating an ocean wave model and a wave boundary model into hurricane-ocean models. It is hypothesized that: (1) Surface momentum fluxes in hurricane conditions strongly depend on the ocean wave fields varying in time and space. The effect of breaking waves is significant under hurricane conditions. Momentum fluxes in hurricane conditions can be predicted accurately by using the CWW model. (2) Hurricane intensity and maximum wind predictions are significantly influenced by the parameterization of the air-sea momentum flux. In particular, the spatial/temporal variability of the drag coefficient has a major influence on predictions. Therefore, the coupling of the CWW model to a hurricane-ocean forecast model will result in a systematic improvement of the forecast skill of hurricane intensity and wind structure.To test these hypotheses, the PIs will perform four specific tasks: (1) incorporate the breaking wave effect into the CWW model, (2) develop a coupled wind-wave-ocean hurricane prediction model by combining the CWW model and the Geophysical Fluid Dynamics Laboratory/University of Rhode Island hurricane-ocean model, (3) investigate how new flux parameterizations affect hurricane intensity, track, and wind structure predictions using both idealized and actual tropical storms, and (4) compare model results with existing and newly obtained experimental data in collaboration with scientists involved in the Office of Naval Research sponsored Coupled Boundary Layers/Air-Sea Transfer (CBLAST) program and Korean Ocean Research Development Institute (KORDI).Broader impacts: This research addresses societal need to better forecast and, thereby, mitigate natural disasters caused by hurricane-generated extreme wind, waves, and rain. The project involves the education and training of a graduate student and post-doctoral scientist. The work promotes international cooperation by using hurricane-observing tower data from KORDI and in turn providing new air-sea modeling techniques to KORDI. The data from the tower will be brought to investigate the air-sea fluxes at high wind speeds and their impact on tropical cyclone predictions through the collaboration with KORDI.