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

飓风活动的频率和严重程度在过去几年里急剧上升。2004年和2005年，几场主要飓风袭击了美国东南海岸，卡特里娜和威尔玛造成的影响是美国历史上损失最大的飓风之一。通常，风暴潮预报的重点是与风引起的岸上漂移和波浪作用有关的局部动力。然而，风暴潮的演变还包括海岸滞留波(CTW)脉冲的近岸传播。线性理论预测，在这种情况下，最强烈的响应发生在下游(在开尔文波传播的意义上)，并在时间上相对于登陆的位置和时刻较晚。这一概念与新奥尔良的情况是一致的，当时卡特里娜飓风登陆密西西比州海岸上游一段距离后几个小时，防护性征兆就被淹没了。2005年10月飓风威尔玛登陆期间，对佛罗里达州西南部海岸收集的唯一和详细的海平面和气压观测将被分析，以描绘出海岸困住波(CTW)脉冲的传播、频散和衰减，当它离开强制区并向下游(向北)移动时。虽然观测阵列不是为了捕捉风暴潮的复杂流体动力学而设计的，但它占据了观察飓风产生的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。数据集由美国地质勘探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。调查区域沿海岸绵延100多公里，仪器部署在海岸线和入海口/河口。这些数据将与现有的NOAA风速和海平面测量结果相补充。将使用大气压力数据来确定风强迫的时间和空间演变：通过应用大气压力变化的结构来外推现有的风的时间序列。还将应用详细的气压测量来准确调整海平面数据，从而探测沿海岸线的CTW脉冲演变。CTW脉冲幅度将仅使用来自暴露的海岸线的数据来确定，而相位将基于来自海岸线和入海口的数据来估计。后者将被及时调整，允许信号以长重力波的速度从嘴向内陆传播。通过应用观测到的强迫并调整底部应力和水平涡旋“粘性”系数，将在模式中再现观测结果，以获得风暴潮的真实传播速度和幅度。陆架地形沿海岸将是统一的，除了上游边界，那里的陆架宽度将突然减小，从而模仿佛罗里达州的南端。弥散、摩擦和非线性的作用将通过与观测到的风力进行实际模型运行以及补充模型在相同的初始扰动(由飓风引起)但作为摩擦大大减少的自由波脉冲、以及具有相同时空结构但具有较小幅度(允许线性弥散)的脉冲的情况下运行来系统地研究。在随后的模型实验中，海岸线特征也将放置在下游，代表卡特里娜飓风(即突出的密西西比河三角洲)的条件。更广泛的影响：数据分析和数值实验的结果将揭示离散、非线性、摩擦衰减和地形变化在飓风登陆驱动的风暴潮近岸演变中的重要性。结果还将提高我们对飓风引发的洪水的理解和可预测性，重点放在下游地区的脆弱性上。

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.