Relative displacement probability distribution functions from balloons and drifters
Relative displacement probability distribution functions from balloons and drifters
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DOI：
10.1357/002224010794657155
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发表时间：
2010-05-01
影响因子：
0.5
通讯作者：
LaCasce, J. H.
中科院分区：
文献类型：
--
作者：
LaCasce, J. H.
大气和海洋中相对（对）分散研究的焦点通常是均方颗粒分离或有限尺度李亚普诺夫指数。尽管对分离的概率密度函数 (PDF) 决定了色散，但人们对它的关注却少得多。在二维 (2-D)、非发散、均匀流中，PDF 由 Fokker-Planck 方程控制。湍流惯性范围存在解析解，但很少与观测结果进行比较。我们考虑湍流惯性范围的解析 PDF，并导出二维能量范围的新解。然后，我们将分析 PDF 与使用三个现场数据集生成的数据进行比较：一个来自平流层的气球实验，两个来自海洋表面漂流器实验。为了进行比较，我们还考虑了中等尺度二维湍流数值模拟的 PDF。结果表明，亚变形尺度上的色散是非局域的，配对分离随时间呈指数增长。这意味着这些尺度的动能谱至少与 kappa(-3) 一样陡。由于较大间距下 PDF 的不确定性，较大尺度的色散更难表征，但结果与之前的推论一致。一般来说，PDF 提供了有关扩散的有用信息，而这些信息很难单独从色散中辨别出来。
The focus of relative (pair) dispersion studies in the atmosphere and ocean is often on the mean square particle separation or the Finite Scale Lyapunov Exponent. Much less attention has been paid to the probability density function (PDF) of pair separations, despite that this determines the dispersion. In two-dimensional (2-D), nondivergent, homogeneous flows, the PDF is governed by a Fokker-Planck equation. Analytical solutions exist for the turbulent inertial ranges, but these have rarely been compared to observations.We consider the analytical PDFs for the turbulent inertial ranges and derive a new solution for the 2-D energy range. We then compare the analytical PDFs with those generated with data from three in situ sets: one from a balloon experiment in the stratosphere and two from surface drifter experiments in the ocean. For comparison, we also consider PDFs from a numerical simulation of 2-D turbulence forced at intermediate scales. The results suggest that dispersion at sub-deformation scales is nonlocal, with pair separations growing exponentially in time. This implies the kinetic energy spectra at these scales are at least as steep as kappa(-3). The dispersion at larger scales is harder to characterize because of the uncertainty in the PDF at larger separations, but the results are consistent with previous inferences. In general the PDF provides useful information on the spreading which can be difficult to discern from the dispersion alone.