Transient Rip Current Dynamics: Laboratory Measurements and Modeling of Surfzone Vorticity

近岸地区，作为重要的潮间带栖息地和娱乐场所的价值，往往受到病原体和过量的营养供应从陆地径流。当一个地区受到污染时，可能会导致海滩关闭、生态破坏和相关的经济损失。了解物质在整个近岸区域的迁移对生态系统和人类健康具有重要意义。以往的研究分析跨大陆架的交换表明，瞬时离岸流是占主导地位的机制驱动碎波带和内大陆架之间的交换。证据还表明，瞬时离岸流是由碎波带涡旋的合并产生的，短峰波是旋转的来源。本项目将利用实验室和数值模拟来研究碎波区涡流的产生和演变，以形成瞬态离岸流。通过这项研究，近岸区域的混合和交换的知识将显着推进，这将对营养物质，幼虫和污染物的运输具有重要意义。将与国家海洋和大气管理局的科学家合作，开发瞬时激流的简单预测器，以改进对各种环境的灾害预测。这是人类安全的重要信息，因为离岸流是海滩上死亡和救援的主要原因。研究生将通过参与这个项目获得宝贵的培训和教育。突出激流的外联活动将作为O.H.欣斯代尔波浪研究实验室推广计划，旨在扩大科学、技术、工程和数学（STEM）的参与。该项目旨在建立一个从摇篮到坟墓的图片，通过短峰波破碎、合并形成更大的漩涡和形成瞬时离岸流，将漩涡注入碎波区。总体目标是确定是否可以将碎波区视为二维湍流箱。这项研究将通过解决四个具体假设，提高对碎波带涡流产生和演变的动力学的理解，从而导致瞬时离岸流和相关的跨大陆架交换：1）短峰波是短时空尺度上重要的涡源; 2）小涡合并形成大涡; 3）碎波带涡的衰减受底摩擦控制;以及4）喷射到碎波带之外的陆架上的涡流偏离二维范例。实验室实验将包括现场和远程（立体可见光和红外）测量海面高度和速度的波高，周期和方向传播的范围。最先进的数值模拟将用于指导实验室取样，分析一系列条件下的动力学，并评估摩擦耗散和三维循环特性的重要性。如果碎波区可以被视为一个强制的二维湍流箱，简化模型与适当的强迫可以建立，以促进了解碎波区在陆地到海洋的运输中的作用。

The nearshore region, valued as essential intertidal habitat and recreational grounds, is often compromised by pathogens and excess nutrient supply from terrestrial runoff. When an area becomes contaminated, beach closures, ecological disruption, and associated economic losses can result. Understanding the transport of materials throughout the nearshore region can have important implications for ecosystem and human health. Previous studies analyzing cross-shelf exchange suggest that transient rip currents are the dominant mechanism driving exchange between the surf zone and the inner shelf. Evidence also suggests that transient rip currents are generated from the coalescence of surf zone eddies, with short-crested waves serving as the source of rotation. This project will utilize a laboratory and numerical modeling to study the generation and evolution of surf zone eddies to form transient rip currents. The knowledge of mixing and exchange in the nearshore region will be significantly advanced through this study, which will have important implications for the transport of nutrients, larvae, and pollutants. In collaboration with National Oceanic and Atmospheric Administration scientists, simple predictors of transient rip currents will be developed to improve hazard forecasts for a broad range of environments. This is essential information for human safety as rip currents are the leading cause of fatalities and rescues on beaches. A graduate student will gain valuable training and education through involvement in this project. Outreach activities highlighting rip currents will be developed as a part of the O.H. Hinsdale Wave Research Laboratory Outreach Program seeking to broaden participation in Science, Technology, Engineering and Mathematics (STEM).This project seeks to establish a cradle-to-grave picture of the injection of eddies into the surf zone by short-crested wave breaking, coalescence to form larger eddies, and formation of transient rip currents. The overall objective is to determine if the surf zone can be treated as a two-dimensional turbulence box. This study will improve understanding of the dynamics of surf zone eddy generation and evolution leading to transient rip currents and associated cross-shelf exchange by addressing four specific hypotheses: 1) short-crested waves are an important vorticity source at short spatial and temporal scales, 2) smaller eddies coalesce to create bigger eddies, 3) surf zone eddy decay is controlled by bottom friction, and 4) eddies ejected outside of the surf zone onto the shelf deviate from the two-dimensional paradigm. Laboratory experiments will include in situ and remote (stereo visible and infrared) measurements of sea-surface-elevations and velocities for a range of wave heights, periods, and directional spreads. State-of-the-art numerical modeling will be used to guide laboratory sampling, to analyze dynamics for a range of conditions, and to assess the importance of frictional dissipation and three-dimensional circulation properties. If the surf zone can be treated as a forced two-dimensional turbulence box, simplified models with appropriate forcing can be established to advance the understanding of the role of the surf zone in land-to-sea transport.