Parameterizations of Lagrangian spin statistics and particle dispersion in the presence of coherent vortices
Parameterizations of Lagrangian spin statistics and particle dispersion in the presence of coherent vortices
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相干涡旋存在下拉格朗日自旋统计和粒子色散的参数化
DOI：
10.1357/002224005775247571
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发表时间：
2005
影响因子：
0.5
通讯作者：
E. Chassignet
中科院分区：
文献类型：
--
作者：
M. Veneziani;A. Griffa;A. Reynolds;Z. Garraffo;E. Chassignet
相干涡在二维和准地转湍流等理想流动的输运过程中起着重要的作用。本文利用高分辨率海洋环流模式模拟的合成拉格朗日资料，在实际海流中研究了它们对涡散和扩散系数的影响。考虑了使用具有非零平均自旋统计量的拉格朗日随机模型(LSM)来参数化观测特征的可能性。还研究了该参数的概率分布(它代表了嵌入在相干涡内的轨迹的循环行为)。结果表明，三峰分布的最小二乘法能较好地再现中、短时间尺度上的涡扩散和频散特征。尤其是相干涡旋的影响，这是由于涡旋的高涡能在短时间内加强了粒子的扩散，而在中间时间由于涡旋捕获机制抑制了扩散。结果表明，旋涡色散的LSM参数化比常用的渐近涡散近似更合适。在LSM中还考虑了比三模更复杂的平均自旋分布，并且发现它们对涡旋统计和色散的预测只产生微小的变化。
Coherent vortices are known to play an important role in transport processes of ideal flows such as two-dimensional and quasi-geostrophic turbulent flows. In this paper, their effect on eddy dispersion and diffusivity is studied in a realistic oceanic flow, using synthetic Lagrangian data simulated within a high-resolution ocean general circulation model in the Gulf Stream recirculation region. The possibility of using a Lagrangian Stochastic Model (LSM) with nonzero mean spin statistic, ,t o parameterize the observed characteristics is considered. The probability distribution of the parameter (which is representative of the looping behavior of trajectories embedded inside the coherent vortices) is also studied. The main result is that the LSM with a tri-modal -distribution is able to reproduce the eddy diffusivity and dispersion characteristics, especially at short and intermediate time scales. Particularly well predicted are the effects of the coherent vortices, which are the enhanced spreading of particles at short times due to the high eddy energy of the vortices and the inhibited diffusion at intermediate times due to the vortex trapping mechanisms. The LSM parameterization of eddy dispersion is shown to be more appropriate than the commonly used asymptotic eddy-diffusivity approximation. More complex than tri-modal distributions of mean spin are also considered in the LSM, and they are found to produce only slight changes in the predictions of eddy statistics and dispersion.