Reconciling float-based and tracer-based estimates of lateral diffusivities
Reconciling float-based and tracer-based estimates of lateral diffusivities
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协调基于浮动和基于示踪剂的横向扩散率估计
DOI：
10.1357/002224012805262743
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发表时间：
2012
影响因子：
0.5
通讯作者：
S. Merrifield
中科院分区：
文献类型：
--
作者：
A. Klocker;R. Ferrari;J. LaCasce;S. Merrifield
横向扩散系数是从合成粒子和示踪剂平流的速度计算
从南太平洋的海面高度测量得出的场，在西太平洋的一个区域，
德雷克海峡。三种不同的估计进行了比较：（1）示踪剂为基础的“有效扩散率”的
中村（1996），（2）示踪云的二阶矩的增长和（3）单和
双粒子拉格朗日扩散系数有效扩散系数测量横流分量
的涡流混合，所以这篇文章的重点是对其他人的对流扩散系数，作为平均流量
(the ACC）在该地区是以区域为导向的。
经过几周的初始瞬态后，有效扩散系数与等效扩散系数吻合良好。
从示踪剂云和颗粒估计的扩散率。这证明了粒子和
基于示踪剂的涡流扩散率的估计是等效的，尽管最近的说法相反。
这三个估计之间的收敛性要求拉格朗日扩散系数估计使用
它们的渐近值，而不是最大值。前者一般比后者低得多。
后者在平均流量的存在下。
对拉格朗日扩散系数的长时间渐近行为进行采样需要非常大的数字
在野外活动中的花车。例如，它表明，将需要数百个浮动，
估算南太平洋一个区域涡动扩散率的垂直和水平变化
海洋
Lateral diffusivities are computed from synthetic particles and tracers advected by a velocity
field derived from sea-surface height measurements from the South Pacific, in a region west of
Drake Passage. Three different estimates are compared: (1) the tracer-based "effective diffusivity" of
Nakamura (1996), (2) the growth of the second moment of a cloud of tracer and (3) the single- and
two-particle Lagrangian diffusivities. The effective diffusivity measures the cross-stream component
of eddy mixing, so this article focuses on the meridional diffusivities for the others, as the mean flow
(the ACC) is zonally oriented in the region.
After an initial transient of a few weeks, the effective diffusivity agrees well with the meridional
diffusivity estimated both from the tracer cloud and from the particles. This proves that particleand
tracer-based estimates of eddy diffusivities are equivalent, despite recent claims to the contrary.
Convergence among the three estimates requires that the Lagrangian diffusivities be estimated using
their asymptotic values, not their maximum values. The former are generally much lower than the
latter in the presence of a mean flow.
Sampling the long-time asymptotic behavior of Lagrangian diffusivities requires very large numbers
of floats in field campaigns. For example, it is shown that hundreds of floats would be necessary to
estimate the vertical and horizontal variations in eddy diffusivity in a sector of the Pacific Southern
Ocean.
影响因子：
3.6
作者：
Garabato, A. C. Naveira;Ferrari, R.;Polzin, K. L.
通讯作者：
Polzin, K. L.