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首页> 外文期刊>Journal of Physical Oceanography >Observing Surf-Zone Dispersion with Drifters
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Observing Surf-Zone Dispersion with Drifters

机译：用漂移仪观察海浪带扩散

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Surf-zone dispersion is studied using drifter observations collected within about 200 m of the shoreline (at depths of less than about 5 m) on a beach with approximately alongshore uniform bathymetry and waves. There were about 70 individual drifter releases, each 10-20 min in duration, on two consecutive days. On the first day, the sea-swell significant wave height H_s was equal to 0.5 m and mean alongshore currents |v| were moderate (< 0.1 m s~(-1)). On the second day, the obliquely incident waves were larger, with H_s equal to 1.4 m, and at some surf-zone locations |v| was greater than 0.5 m s~(-1). The one-particle diffusivity was larger, with larger waves and stronger currents. On both days, the one-particle diffusivity tensor is noniso-tropic and time-dependent. The major axis is initially parallel to the cross-shore direction, but after a few wave periods it is aligned with the alongshore direction. In both the along- and cross-shore directions, the asymptotic diffusivity is reached sooner within, rather than seaward of, the surf zone. Two-particle statistics indicate that relative dispersion grows like D~2(t) ~ t~(3/2) and that the relative diffusivity is scale-dependent as μ ～ l~(2/3), with / being the particle separation. The observed scalings differ from 2D inertial-subrange scalings [D~2(t) ~ t~3 and μ ~ l~(4/3)]. Separations have a non-Gaussian self-similar distribution that is independent of time. The two-particle statistics are consistent with a nonconstant-coefficient diffusion equation for the separation probability density functions. The dispersion is explained by neither irrotational surface gravity waves nor shear dispersion. The observations imply the existence of a 2D eddy field with 5-50-m length scales, the source of which is speculated to be alongshore gradients in breaking-wave height associated with finite crest lengths.
机译：使用在海滩上约200 m处（小于约5 m的深度处）收集的漂流观测资料研究海浪区的分散性，并采用沿岸均匀的测深法和海浪。在连续两天中，大约有70个单独的流浪者释放，每次持续10-20分钟。在第一天，海浪有效波高H_s等于0.5 m，平均沿岸水流| v |。中等（<0.1 m s〜（-1））。在第二天，斜入射波更大，H_s等于1.4 m，并且在某些冲浪区位置| v |处。大于0.5 m s〜（-1）。单粒子扩散率更大，波更大，电流更强。在这两天中，单粒子扩散张量都是非各向同性的，并且与时间有关。主轴线最初平行于跨岸方向，但经过几个波浪周期后，它与沿岸方向对齐。在沿海岸和跨海岸的方向上，渐近扩散率都是在冲浪区域内而不是向海的较早到达的。两粒子统计表明，相对色散随着D〜2（t）〜t〜（3/2）的增长而增长，相对扩散率与尺度相关，为μ〜l〜（2/3），其中/为粒子间距。观测到的标度不同于二维惯性子范围标度[D〜2（t）〜t〜3和μ〜l〜（4/3）]。分隔具有与时间无关的非高斯自相似分布。两粒子统计与分离概率密度函数的非常数扩散方程一致。既不用旋转表面重力波也不用剪切力分散来解释色散。这些观测结果暗示存在一个长度为5-50米的2D涡流场，据推测其来源是与有限波峰长度相关的破碎波高度的沿岸梯度。

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