SGER: Transient Shelf Response to the Hurricane Wilma's Impact

在过去几年中，飓风活动的频率和严重程度急剧上升。2004年和2005年，几次大型飓风袭击了美国东南海岸，其中卡特里娜飓风和威尔玛飓风造成的损失是美国历史上最严重的。通常，风暴潮预测集中在与风引起的陆上漂移和波浪作用相关的局部动力学上。然而，风暴潮的演变还包括海岸困波脉冲的沿岸传播。线性理论预测，在这种情况下，最强烈的反应发生在下游（在开尔文波传播的意义上），并且相对于登陆的位置和时刻晚一些。这种观点与新奥尔良发生的事件是一致的，当时卡特里娜飓风在上游一段距离的密西西比河海岸登陆几小时后，保护性的堤坝就被淹没了。在2005年10月飓风“威尔玛”登陆期间，将对佛罗里达西南海岸收集的海平面和气压的独特而详细的观测资料进行分析，以描绘海岸捕获波（CTW）脉冲在离开强迫区并向下游（向北）移动时的传播、扩散和衰减。虽然观测阵列的设计不是为了捕捉风暴潮的复杂流体动力学，但它占据了观测飓风产生的CTW脉冲的最佳位置。这些数据还将用于调整原始方程模型，以便对飓风对宽浅大陆架的影响进行面向过程的研究。该数据集由美国地质调查局佛罗里达综合科学中心在大约30个地点测量的风暴潮(S)和气压(B)的一周时间序列组成。调查区域横跨海岸100多公里，仪器部署在海岸线和入口/河口。这些数据将与NOAA现有的风和海平面测量数据相结合。大气压数据将用于确定风强迫的时空演变：可用的风时间序列将通过应用大气压变化的结构来外推。详细的气压测量也将被应用于精确调整海平面数据，从而探测沿海岸线的CTW脉冲演变。CTW脉冲幅度将仅通过使用来自暴露海岸线的数据来确定，而相位将根据来自海岸线和进口的数据来估计。后者将通过允许信号以长重力波的速度从河口向内陆传播来及时调整。为了获得风暴潮的真实传播速度和振幅，将应用观测到的强迫和调整底部应力和水平涡“粘度”系数来复制观测结果。除了上游边界外，陆架地形在沿岸将是均匀的，在上游边界，陆架宽度将突然减小，从而模仿佛罗里达州的南端。色散、摩擦和非线性的作用将通过对观测到的风强迫和具有相同初始扰动（由飓风引起）但作为摩擦大大减少的自由波脉冲传播的实际模型运行进行系统研究，也将作为具有相同时空结构但振幅较小（允许线性色散）的脉冲运行。在后续的模型实验中，海岸线特征也将被放置在下游，代表卡特里娜飓风的情况（即突出的密西西比三角洲）。更广泛的影响：数据分析和数值实验的结果将揭示频散、非线性、摩擦衰减和地形变化在飓风登陆引起的风暴潮沿岸演变中的重要性。研究结果还将提高我们对飓风引发的洪水的理解和可预测性，重点关注下游地区的脆弱性。

The frequency and severity of hurricane activity has risen sharply over the last few years. Several major hurricanes hit the US Southeast coast in the 2004 and 2005 seasons, with the impacts from Katrina and Wilma being among the costliest in the US history. Typically, the storm surge predictions are focused on local dynamics associated with the wind-induced onshore drift and the wave action. However, the evolution of storm surge also includes an alongshore propagation of the coastally trapped wave (CTW) pulse. Linear theories predict that in such a case the strongest response occurs downstream (in the sense of Kelvin wave propagation) and later in time relative to the location and moment of the landfall. This notion is consistent with the events in New Orleans, when the protective levies were overwhelmed a few hours after the Hurricane Katrina's landfall some distance upstream, on the Mississippi coast.Unique and detailed observations of sea level and barometric pressure along the Southwest Florida coast collected during Hurricane Wilma's landfall in October 2005 will be analyzed to delineate the coastally trapped wave (CTW) pulse propagation, dispersion and decay as it leaves the forcing region and moves downstream (northward). While the observational array was not designed to capture the complex hydrodynamics of the storm surge, it occupied an optimal position for observing the hurricane-generated CTW pulse.. These data will also be used for tuning-up the primitive equation model in order to conduct a process-oriented study of the hurricane's impact on the wide and shallow shelf. The data set consists of weeklong time series of storm surge (S) and barometric pressure (B) measured by the USGS Florida Integrated Science Center at approximately 30 locations. The survey area spanned more than 100 km alongshore with the instruments deployed both on the coastline and in the inlets/estuaries. These data will be augmented with the existing NOAA wind and sea level measurements. The atmospheric pressure data will be used in order to determine a temporal and spatial evolution of the wind forcing: the available time series of wind will be extrapolated by applying the structure of atmospheric pressure variations. Detailed barometric pressure measurements will be also applied to accurately adjust the sea level data and thus to detect the CTW pulse evolution along the coastline. The CTW pulse amplitude will be determined by using data from the exposed coastline only, while the phase will be estimated based both on data from the coastline and from the inlets. The latter will be adjusted in time by allowing the signal propagation from the mouth inland at a speed of a long gravity wave. The observations will be reproduced in the model by applying the observed forcing and tuning the bottom stress and horizontal eddy "viscosity" coefficients in order to obtain a realistic propagation speed and amplitude of the storm surge. The shelf topography will be uniform alongshore, except for the upstream boundary, where the shelf width will diminish abruptly, thus mimicking the southern tip of Florida. The role of dispersion, friction and nonlinearity will be systematically studied by conducting realistic model runs with the observed wind forcing and complimentary model runs with the same initial disturbance (induced by the hurricane) but traveling as a free wave pulse with much reduced friction, and also as a pulse of the same spatial-temporal structure but with a smaller amplitude (allowing linear dispersion). In subsequent model experiments, the coastline feature will also be placed downstream, representing the conditions of Hurricane Katrina (i.e., protruding Mississippi delta). Broader Impacts: The results of data analysis and numerical experiments will reveal the importance of dispersion, nonlinearity, frictional decay and topographic variations in the alongshore evolution of storm surge driven by a hurricane landfall. The results will also improve our understanding and predictability of hurricane-induced flooding with a focus on vulnerability of the downstream areas.