High-Resolution Observations of the North Pacific Transition Layer from a Lagrangian Float
High-Resolution Observations of the North Pacific Transition Layer from a Lagrangian Float
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DOI：
10.1175/jpo-d-21-0032.1
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发表时间：
2021-10-01
影响因子：
3.5
通讯作者：
Harcourt, Ramsey R.
中科院分区：
文献类型：
--
作者：
Kaminski, Alexis K.;D'Asaro, Eric A.;Harcourt, Ramsey R.
海洋表面边界层（OSBL）的一个关键区域是将混合层与上部密度跃层分离的强烈剪切和强烈分层的过渡层（TL），其中可能存在各种波动和不稳定性。以前的工作表明，这些不同的波和不稳定性将导致不同的OSBL行为。因此，理解发生的物理过程是TL建模的关键。在这里，我们介绍了2018年秋季在海洋气象站Papa（50度N，145度W）附近部署了73天的拉格朗日浮子的TL观测结果。浮标跟随TL的垂直运动，使用ADCP，温度链和盐度传感器连续测量剖面。温度链制作了TL结构的深度-时间图像，分辨率为6 cm和3 s。这些结果表明，非常尖锐的界面经常出现，主要是温度在6厘米或更小的范围内跳跃0（1）摄氏度。温度反转通常很小（小于或接近10厘米），频繁，并且强烈分层;很少观察到大的反转。相应的速度分布在更大的长度尺度上变化比温度分布。这些结构与冲刷行为一致，而不是Kelvin-Helmholtz型倾覆。通过索普尺度分析估计的净效应表明，这些频繁的小逆温可以解释观测到的混合层加深和夹带通量。耗散，扩散率和热通量的相应估计也同意与以前的TL研究，这表明TL动力学是由这些几乎连续的10厘米尺度的混合结构，而不是不太频繁的较大的翻转。
A crucial region of the ocean surface boundary layer (OSBL) is the strongly sheared and strongly stratified transition layer (TL) separating the mixed layer from the upper pycnocline, where a diverse range of waves and instabilities are possible. Previous work suggests that these different waves and instabilities will lead to different OSBL behaviors. Therefore, understanding which physical processes occur is key for modeling the TL. Here we present observations of the TL from a Lagrangian float deployed for 73 days near Ocean Weather Station Papa (50 degrees N, 145 degrees W) during fall 2018. The float followed the vertical motion of the TL, continuously measuring profiles across it using an ADCP, temperature chain, and salinity sensors. The temperature chain made depth-time images of TL structures with a resolution of 6 cm and 3 s. These showed the frequent occurrence of very sharp interfaces, dominated by temperature jumps of O(1)degrees C over 6 cm or less. Temperature inversions were typically small (less than or similar to 10 cm), frequent, and strongly stratified; very few large overturns were observed. The corresponding velocity profiles varied over larger length scales than the temperature profiles. These structures are consistent with scouring behavior rather than Kelvin-Helmholtz-type overturning. Their net effect, estimated via a Thorpe-scale analysis, suggests that these frequent small temperature inversions can account for the observed mixed layer deepening and entrainment flux. Corresponding estimates of dissipation, diffusivity, and heat fluxes also agree with previous TL studies, suggesting that the TL dynamics is dominated by these nearly continuous 10-cm-scale mixing structures, rather than by less frequent larger overturns.