Semidiurnal Perturbations to Storm Surges on the U.S. Eastern Seaboard

半日扰动修改了飓风桑迪(2012)和艾琳(2011)的非潮汐涌动，影响了整个美国东海岸。在南大西洋海湾，扰动的幅度高达总涌浪幅度的50%-60%。一般来说，当从观测水位中减去预测水位时，半日扰动变得明显。这种潮汐-潮汐相互作用的反应是改变潮汐低水位和高水位的时间，预计这与接近递进到接近静止的潮汐不同。该项目旨在促进对触发风暴潮半日扰动并确定扰动大小的过程的了解。大气强迫可以通过直接的地表应力以及通过诱发额外的底部应力和潮汐应力来干扰涌浪。每种压力的相对贡献需要更好的理解。这项调查的具体目标是确定a)是否在其他热带风暴和温带风暴下出现半日扰动，b)与扰动有关的动力因素的相对大小，以及c)产生扰动的大气和潮汐强迫阈值。具体目标将通过美国东海岸潮汐和气象站的观测，以及现实和面向过程的数值模拟来解决。智慧的优点：近几十年来，世界各地的沿海地区受到风暴的影响，这些风暴导致严重的洪水、建筑物损坏和海滩侵蚀。风暴-潮汐相互作用有时可产生与风暴相关的最高水平，与涨潮无关，但仍处于半日周期。因此，有必要了解风暴引发的半日扰动的行为，以便改进风暴潮的预报和预警系统。这个项目将试图回答几个关键问题：沿美国东部移动的每一场风暴都会发生半日扰动吗？东北风期间也会发生半日扰动吗？与这些扰动相关的动力是什么？有没有大气强迫阈值，低于这个阈值，这些扰动就消失了？扰动依赖于潮汐幅度吗？半日摄动的峰值是否在潮汐周期的某一阶段持续发展？显然，有必要了解触发涌浪的半日扰动的适当条件。这项研究产生的结果将有助于理解高频(周期小于惯性周期)扰动的出现原因，半日残差会改变风暴的运行。更广泛的影响：这个项目将研究一种可能影响整个美国东海岸的现象。由于南大西洋海湾的半日摄动可以达到总涌浪信号的50%-60%，因此必须考虑潮汐与涌浪的相互作用。这些相互作用也将影响最大涨潮的时间，相对于涨潮。因此，与风暴潮到达有关的概率密度函数将受到半日残差的影响。更好地了解这些扰动将有助于完善对整个美国东海岸的风暴潮预测和风险分析。该项目将通过长达一学期的研究经验支持一名研究生、一名本科生，以及一名高中生通过暑期实习。这名高中生将被招募到佛罗里达州盖恩斯维尔高中的少数族裔群体中。这个项目的结果将被介绍给K-12的观众，并将被纳入佛罗里达大学私人投资机构的课堂。这两个私营部门的参与加强了代表不足的群体对科学的参与。

Semidiurnal perturbations modified the non-tidal surges of hurricanes Sandy (2012) and Irene (2011) which affected the entire U.S. eastern seaboard. In the South Atlantic Bight, the amplitude of the perturbations reached up to 50-60% of the total surge amplitude. In general, semidiurnal perturbations become evident when predicted water levels are subtracted from observed water levels. A response of such tide-surge interaction is to modify the timing of tidal low and high water, which is expected to be different from nearly progressive to nearly standing tides. This project seeks to advance understanding of the processes that trigger semidiurnal perturbations on storm surges and that determine the size of the perturbations. Atmospheric forcing can disturb the surge through direct surface stress and by inducing additional bottom stress and tidal stress. The relative contribution of each stress needs improved understanding. Specific objectives of this investigation are to determine a) whether semidiurnal perturbations appear under other tropical storms and under extratropical storms, b) the relative size of the dynamic agents associated with the perturbations, and c) the atmospheric and tidal forcing thresholds that produce them. Specific objectives will be addressed with observations from tidal and meteorological stations along the U.S. eastern coast, and with realistic and process-oriented numerical simulations.Intellectual Merit: In recent decades, coastal areas worldwide have been affected by storms that cause severe flooding, damage to buildings, and beach erosion. Storm-tide interactions can produce the highest storm-related levels at times not linked to high tide but still at semidiurnal periodicities. It is therefore necessary to understand the behavior of semidiurnal perturbations triggered by storms in order to improve forecasts and warning systems of storm surges. This project will try to answer several key questions: Do semidiurnal perturbations occur in every storm that moves along the eastern US? Do semidiurnal perturbations also occur during nor'easters? What are the dynamics associated with these perturbations? Are there atmospheric forcing thresholds below which these perturbations vanish? Do perturbations depend on the tidal amplitude? Does the peak in semidiurnal perturbations develop consistently in one phase of the tidal cycle? Clearly, there is a need to understand appropriate conditions for triggering semidiurnal perturbations on the surge. Findings generated from the study will help understand the causes for the appearance of high frequency (periods smaller than the inertial period) perturbations, semidiurnal residuals, which modify storm surges.Broader Impacts: This project will study a phenomenon that can affect the entire U.S. eastern seaboard. Because semidiurnal perturbations can reach amplitudes of up to 50-60% of the total surge signal in the South Atlantic Bight, it is imperative to include tide-surge interactions. These interactions will also affect the timing of maximum surge, relative to high tide. Probability density functions related to arrival of storm surges will thus be affected by semidiurnal residuals. Better understanding of these perturbations will help to refine storm surge predictions and risk analysis for the entire eastern U.S. seaboard. The project will support one graduate student, one undergraduate, through semester-long research experiences, and one high school student through summer internships. The high school student will be recruited among minority groups among high schools in Gainesville, Florida. Results derived from this project will be presented to K-12 audiences and will be incorporated in classes taught by the PIs at the University of Florida. The involvement of both PIs enhances the participation of underrepresented groups in science.