Torrey Pines Beach Nearshore Waves

Nearshore waves at Torrey Pines Beach. To facilitate modeling of beach profile change, wave characteristics in 10m depth spaced 100m alongshore were extracted from the Scripps Institution of Oceanography’s wave Monitoring and Prediction (MOP) system for the California coastline (http://cdip.ucsd.edu/). Wave estimates along the coastline are produced using a linear spectral refraction model initialized with 2-D spectral estimates from multiple Datawell directional buoys. For swell waves (0.04–0.08 Hz) the model is initialized with deep water buoys located seaward of the Channel Islands. For sea waves (0.09-0.5 Hz) the model is initialized with buoys located inside the islands along the mainland shelf break. Each MOP point in 10m depth has a corresponding backbeach point, defining a MOP line. MOP line orientations are chosen to minimize the distance from the backbeach to the 10m contour. Hindcast time series of wave height (H_s), peak (T_p) and average (T_a) wave period, peak (D_p) and mean (D_m) wave direction, and radiation stress estimates (onshore S_{xx} and alongshore S_{xy}) are provided at each transect line relative to the MOP estimated shore normal (orientation also provided). Additionally, time series of wave energy, E, and low-order moment directional Fourier coefficients (a_1, b_1, a_2, b_2, in true compass “from” coordinates), as a function of wave frequency, are provided at the seaward end of each MOP line on the 10m depth contour. The 10m depth wave model output mirrors the information provided by directional wave buoys or a pressure-velocity meter (PUV), and can be treated in the same way as the spectral data from these instruments when defining boundary conditions for sediment transport models. Occasionally, wave model output is degraded due to buoy malfunctions and is flagged using the "waveFlagPrimary" variable. (Good model output has waveFlagPrimary = 1.) WHEN USING THE MODEL OUTPUT IT IS IMPERATIVE THAT THE WAVEFLAGPRIMARY IS CONSIDERED IN CONJUNCTION WITH THE WAVE ESTIMATES. The nearshore wave hindcasts were validated using shallow water wave buoys (20m depth). The hourly buoy-driven wave hindcasts show significant skill at most validation sites, but prediction errors for individual swell or sea events can be large. Model skill is high at the sites in north San Diego County. Overall, the buoy-driven model hindcasts have relatively low bias such that averaging over space or time is useful for minimizing noise. Best practices for using the 100m spaced, 10m depth MOP wave hindcasts, as boundary conditions for beach change models, are not well established. It is not known if alongshore averaging or smoothing of the 100m-spaced MOP hindcasts (eg. on typical sea, swell or infragravity wavelength scales) is beneficial for beach change model stability. Space-time wave averaging questions must be explored by investigators based on their specific modeling needs and goals. Using the fixed shore normal S_{xy} estimates with 2D beach change models that predict changes in shoreline orientation is internally inconsistent, so additional second-order rotations of the S_{xy} values (or direct recalculation of S_{xy} using the a_2 and b_2 Fourier coefficients in compass coordinates) based on modeled shore normal changes, will be required.

本数据集为托里松海滩（Torrey Pines Beach）近岸海浪数据。为支撑海滩剖面变化模拟研究，研究人员从美国斯克里普斯海洋研究所（Scripps Institution of Oceanography）面向加州海岸线搭建的海浪监测与预报（MOP）系统（http://cdip.ucsd.edu/）中，提取了沿岸间距100米、水深10米处的海浪特征参数。该沿岸海浪估算结果基于线性频谱折射模型生成，模型初始条件由多台Datawell测向浮标的二维频谱观测数据提供。其中，对于涌浪（频率范围0.04–0.08 Hz），模型以海峡群岛（Channel Islands）向海侧的深水浮标数据作为初始场；对于风浪（频率范围0.09–0.5 Hz），模型以大陆架坡折带沿岸、海峡群岛内侧的浮标数据作为初始场。每个位于10米水深的MOP测点对应一处后滩测点，共同构成一条MOP断面线。MOP断面线的取向以最大化后滩至10米等深线的距离为原则确定。每条断面线均提供了以下后报时间序列数据：有效波高（significant wave height, H_s）、峰值周期（T_p）与平均周期（T_a）、峰值波向（D_p）与平均波向（D_m），以及辐射应力估算值（岸向S_{xx}与沿岸S_{xy}），所有数据均以MOP估算的岸法线方向为基准（断面取向信息同步提供）。此外，每条MOP断面线的10米等深线向海端，还提供了随波频率变化的海浪能量E，以及低阶矩方向傅里叶系数（a_1, b_1, a_2, b_2，采用真北"来向"坐标系）。10米水深海浪模型的输出结果与测向浮标或压力-速度计（PUV）的观测数据格式一致，在为泥沙输运模型定义边界条件时，可直接采用与这类仪器频谱数据相同的处理方式。受浮标故障影响，部分海浪模型输出结果存在质量问题，可通过"waveFlagPrimary"变量进行标记（优质模型输出的waveFlagPrimary值为1）。使用该模型输出时，必须结合waveFlagPrimary变量对海浪估算结果进行质量校验。本近岸海浪后报数据已通过20米水深的浅海海浪浮标进行了验证。逐小时浮标驱动的海浪后报结果在多数验证站点均表现出较好的模拟能力，但针对单个涌浪或风浪事件的预测误差可能较大。圣迭戈县北部站点的模型模拟精度较高。总体而言，浮标驱动的模型后报结果偏差较低，通过空间或时间平均可有效抑制噪声。目前，将该沿岸间距100米、水深10米的MOP海浪后报数据作为海滩变化模型边界条件的最佳实践尚未明确。尚不明确对100米间距的MOP后报数据进行沿岸平均或平滑处理（例如基于典型风浪、涌浪或亚重力波波长尺度）是否有助于提升海滩变化模型的稳定性。相关时空海浪平均的技术方案需研究者根据具体的模拟需求与目标自行探索。若采用固定岸法线方向的S_{xy}估算值开展岸线走向预测的二维海滩变化模型研究，会存在内在逻辑不一致的问题，因此需基于模拟得到的岸法线变化对S_{xy}值进行二阶旋转修正（或采用罗盘坐标系下的a_2、b_2傅里叶系数直接重新计算S_{xy}）。