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

半日扰动改变了飓风桑迪（2012年）和艾琳（2011年）的非潮汐浪涌，影响了整个美国东海岸。在南大西洋湾，扰动的幅度达到总涌浪幅度的50-60%。一般来说，半日扰动变得明显时，预测水位从观测水位。这种潮涌相互作用的一个响应是修改潮汐低潮和高潮的时间，预计这将是不同的接近进步接近站立的潮汐。该项目旨在增进对引发风暴潮半日扰动和确定扰动大小的过程的了解。大气强迫可以通过直接的表面应力和诱导额外的海底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。 本次调查的具体目标是确定a）半日扰动是否出现在其他热带风暴和温带风暴下，B）与扰动相关的动力因子的相对大小，以及c）产生它们的大气和潮汐强迫阈值。具体目标将与观测从潮汐和气象站沿着美国东部海岸，并与现实和面向过程的数值模拟。智力优点：在最近几十年来，全球沿海地区受到风暴的影响，造成严重的洪水，建筑物的损坏，和海滩侵蚀。风暴潮相互作用可以产生最高的风暴相关水平的时间不与高潮，但仍然在半日周期。因此，有必要了解风暴引起的半日扰动的行为，以改善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：半日扰动是否发生在沿着美国东部移动的每一个风暴中？半日扰动也发生在东北风期间吗？与这些扰动相关的动力学是什么？是否存在大气强迫阈值，低于该阈值，这些扰动就会消失？扰动依赖于潮汐振幅吗？半日扰动的峰值是否始终在潮汐周期的一个相位中发展？显然，有必要了解适当的条件，触发半日扰动的激增。研究结果将有助于理解高频率（周期小于惯性周期）扰动和半日残差出现的原因，这些扰动会改变风暴潮。更广泛的影响：该项目将研究一种可能影响整个美国东海岸的现象。由于半日扰动可以达到的幅度高达50-60%的总浪涌信号在南大西洋湾，它是必要的，包括潮汐浪涌的相互作用。这些相互作用也将影响相对于高潮的最大浪涌的时间。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整个美国东部沿海地区的风暴潮预测和风险分析。该项目将支持一名研究生，一名本科生，通过为期一个学期的研究经验，并通过暑期实习一名高中生。这名高中生将在佛罗里达盖恩斯维尔的高中少数民族中招募。从这个项目得出的结果将被提交给K-12观众，并将被纳入由PI在佛罗里达大学教授的课程。这两个PI的参与提高了代表性不足的群体在科学中的参与。

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.