Physics of diurnal warm layers : turbulence, internal waves, and lateral mixing
Physics of diurnal warm layers : turbulence, internal waves, and lateral mixing
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昼夜暖层物理学：湍流、内波和横向混合
DOI：
10.1575/1912/8524
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发表时间：
2017
影响因子：
--
通讯作者：
A. Bogdanoff
中科院分区：
文献类型：
--
作者：
A. Bogdanoff
当风小且太阳日照强时，太阳对海洋的每日加热可以形成稳定的近表层分层。这种类型的浅稳定层被称为日暖层（DWL）。本文利用副热带北大西洋的观测资料，结合上层海洋区域研究（sprs - i）的盐度过程，研究了重漂的物理和动力学。通过风应力从大气转移到海洋的动量被困在DWL中，产生横过该层的切变。在sprs - i期间，近地表滑翔机微观结构剖面观测到的湍流动能（TKE）耗散（ε, ε > 10−5 W/kg）增强与强日切变同时发生。然而，尺度分析表明，地表强迫，包括日切变，可能不是TKE耗散增强的唯一机制。高频率内波（ω f）在白天海上观测到。内波能够通过未分层的残余混合层（DWL和季节性温跃层之间的中间层）将能量从深海传递到DWL。随着DWL层化强度的增大，隧道内波引起的剪切也随之增大。分析表明，内波可以产生足够强的剪切，从而引起剪切引起的不稳定，并且可能是观测到的增强TKE耗散的来源。发生垂直变化的上层海洋水平输送是因为在DWL内存在日流，而在下面的非分层残余混合层中不存在日流。因此，当存在DWL时，DWL内的水水平输送距离与下面的水不同。再加上夜间对流将DWL与非分层层混合在一起，这个循环是亚中尺度（1-10公里）横向扩散穿过上层海洋的机制。水平扩散系数估计值的大小与目前基于观测的亚中尺度扩散估计值相似，可能是上层海洋水平扩散的一个重要来源。论文导师：J. Thomas Farrar职称：Woods Hole海洋研究所副科学家论文导师：Carol Anne Clayson职称：Woods Hole海洋研究所高级科学家
The daily heating of the ocean by the sun can create a stably stratified near-surface layer when the winds are slight and solar insolation is strong. This type of shallow stable layer is called a Diurnal Warm Layer (DWL). This thesis examines the physics and dynamics of DWLs from observations of the subtropical North Atlantic Ocean associated with the Salinity Processes in the Upper ocean Regional Study (SPURS-I). Momentum transferred from the atmosphere to the ocean through wind stress becomes trapped within the DWL, generating shear across the layer. During SPURS-I, strong diurnal shear across the DWL was coincident with enhanced turbulent kinetic energy (TKE) dissipation (ε, ε > 10−5 W/kg) observed from glider microstructure profiles of the near-surface. However, a scale analysis demonstrated that surface forcing, including diurnal shear, could not be the sole mechanism for the enhanced TKE dissipation. High-frequency internal waves (ω ≫ f) were observed in the upper ocean during the daytime within the DWL. Internal waves are able to transfer energy from the deep ocean into the DWL through the unstratified remnant mixed layer, which is the intervening layer between the DWL and seasonal thermocline. As the strength of the stratification of the DWL increases, so does the shear caused by the tunneling internal waves. The analysis demonstrates that internal waves can generate strong enough shear to cause a shear-induced instability, and are a plausible source of the observed enhanced TKE dissipation. Vertically-varying horizontal transport across the upper ocean occurs because a diurnal current exists within the DWL, but not in the unstratified remnant mixed layer below. Therefore, when a DWL is present, the water within DWL is horizontally transported a different distance than the water below. Coupled with nocturnal convection that mixes the DWL with the unstratified layer at night, this cycle is a mechanism for submesoscale (1-10 km) lateral diffusion across the upper ocean. Estimates of a horizontal diffusion coefficient are similar in magnitude to current estimates of submesoscale diffusion based on observations, and are likely an important source of horizontal diffusion in the upper ocean. Thesis Supervisor: J. Thomas Farrar Title: Associate Scientist, Woods Hole Oceanographic Institution Thesis Supervisor: Carol Anne Clayson Title: Senior Scientist, Woods Hole Oceanographic Institution
影响因子：
13.5
作者：
Owen Embury;C. Merchant;G. Corlett
通讯作者：
Owen Embury;C. Merchant;G. Corlett
影响因子：
8
作者：
Donlon, C.;Robinson, I.;Rayner, N.
通讯作者：
Rayner, N.