Time Scales of Submesoscale Flow Inferred from a Mooring Array
Time Scales of Submesoscale Flow Inferred from a Mooring Array
复制标题
DOI：
10.1175/jpo-d-19-0254.1
复制
发表时间：
2020-04
影响因子：
3.5
通讯作者：
J. Callies;R. Barkan;A. N. Garabato
中科院分区：
文献类型：
--
作者：
J. Callies;R. Barkan;A. N. Garabato
虽然动能在亚中尺度范围（1-100 km）的空间分布已经从观测中估计出来，但相关的时间尺度在很大程度上是不受限制的。这些时间尺度可以为亚中尺度湍流动力学提供重要的见解，因为它们有助于量化流在多大程度上是亚惯性的，从而受到地球自转的限制。这里使用系泊阵列来估计东北大西洋的这些时间尺度。频率分辨结构函数表明，在10公里左右的空间尺度上，冬季高能亚中尺度湍流在大约1天的时间尺度上演变。虽然这些时间尺度与惯性周期相当，但观测到的流动也显示出亚惯性流动的特征，即地转平衡到领先顺序。近似的亥姆霍兹分解表明，10公里量级的流由其旋转分量主导，这些尺度上的均方根罗斯比数估计为0.3。这种旋转优势和低于1的罗斯比数持续到2.6公里，这是系泊阵列可以达到的最小空间尺度，尽管实际上是超惯性欧拉演化。这表明亚中尺度湍流的拉格朗日演化比系泊估算的欧拉时间尺度要慢。因此，观测结果表明，平均而言，亚中尺度湍流在1 - 100公里范围内很大程度上遵循亚惯性动力学，即使多普勒频移产生超惯性欧拉演化。随着尺度的缩小，地转运动对亚中尺度湍流的演化越来越重要，在2.6 km的空间尺度上，均方根罗斯比数达到0.5。
While the distribution of kinetic energy across spatial scales in the submesoscale range (1–100 km) has been estimated from observations, the associated time scales are largely unconstrained. These time scales can provide important insight into the dynamics of submesoscale turbulence because they help quantify to what degree the flow is subinertial and thus constrained by Earth’s rotation. Here a mooring array is used to estimate these time scales in the northeast Atlantic. Frequency-resolved structure functions indicate that energetic wintertime submesoscale turbulence at spatial scales around 10 km evolves on time scales of about 1 day. While these time scales are comparable to the inertial period, the observed flow also displays characteristics of subinertial flow that is geostrophically balanced to leading order. An approximate Helmholtz decomposition shows the order 10-km flow to be dominated by its rotational component, and the root-mean-square Rossby number at these scales is estimated to be 0.3. This rotational dominance and Rossby numbers below one persist down to 2.6 km, the smallest spatial scale accessible by the mooring array, despite substantially superinertial Eulerian evolution. This indicates that the Lagrangian evolution of submesoscale turbulence is slower than the Eulerian time scale estimated from the moorings. The observations therefore suggest that, on average, submesoscale turbulence largely follows subinertial dynamics in the 1–100-km range, even if Doppler shifting produces superinertial Eulerian evolution. Ageostrophic motions become increasingly important for the evolution of submesoscale turbulence as the scale is reduced—the root-mean-square Rossby number reaches 0.5 at a spatial scale of 2.6 km.