Collaborative Research: Isopycnal Spectra and Stirring on the Submesoscale and Finescale in the Upper Ocean

侧向搅拌是决定上层海洋中水团性质、营养物质和溶解气体的分布和命运的主要过程之一，与平流和昼夜混合一起。海洋环流模式可解决30公里以上尺度的搅动，区域模式可分辨近1公里尺度的搅动，但仍需对未分辨的亚中尺度过程的等周期搅动进行参数化。亚热带太平洋的新的高分辨率观测将提供对基本物理和这些过程如何在上层海洋中运行的洞察，以便改进涡旋分辨海洋环流模式的这种参数化。结果应该适用于其他旋转分层流体的亚中尺度，如地球的大气，恒星和气态巨星占据相同的参数空间。一名博士后将接受关于海洋次中尺度这一迅速崛起领域的数据解释方面的培训。两名研究生将有机会参与航海研究。一阶Rossby数和梯度Richardson数亚惯性流作为海洋参数空间的一个区域出现，人们对此尚不完全了解，但已被观测、建模和理论所了解。由于观测约束的缺乏，在小于Rossby变形长度约100千米、长于外部湍流尺度约1米的长度尺度上的等速搅拌的运动学和动力学没有良好的理论支持。准地转(QG)理论预测，在比Rossby长度尺度更短的尺度上，示踪剂的谱斜率应为负1[对应于斜率为正1的示踪剂梯度谱]。这与横跨水平波长30米至500公里的众多观测结果形成鲜明对比，这些观测报告在该波数带上的示踪梯度光谱明显更红，而且通常几乎是平坦的。类似的动态比较供不应求。海洋上层150米的高分辨率部分将使用拖链进行采样，拖链带有紧密间隔的温度、电导率和压力(CTD)传感器和船上的声学多普勒海流剖面仪(ADCP)。该项目将把被动示踪剂(水团、SPICE、盐度异常)在等压线上的水平波数谱特征化为比以前完成的更高的水平波数，并解决在这些尺度上引起搅拌的亚惯性O(1公里)水平应变张量思想，以及确定应变时间尺度。这些测量将提供对一阶Rossby数和Richardson数流的关键观测约束。

Lateral stirring is among the primary processes, along with advection and diapycnal mixing, that determines the distribution and fate of water-mass properties, nutrients and dissolved gases in the upper ocean. Ocean general circulation models resolve stirring on scales larger than thirty kilometers, and regional models on scales close to one kilometer, but isopycnal stirring by unresolved submesoscale processes must still be parameterized. Novel high-resolution observations in the sub-tropical Pacific Ocean will provide insight into the underlying physics and how these processes operate in the upper ocean in order to improve such parameterizations for eddy-resolving ocean circulation models. Results should be applicable to the submesoscale in other rotating stratified fluids such as the atmosphere of Earth, stars and gas giants that occupy the same parameter space. A post-doctoral fellow will be trained in interpretation of data in the rapidly emerging field of oceanic submesoscales. Two graduate students will have an opportunity to participate in sea-going research.Order one Rossby number and gradient Richardson number sub-inertial flows have emerged as an area of ocean parameter space that is incompletely understood but becoming accessible to observations, modelling and theory. The kinematics and dynamics of isopycnal stirring on length scales shorter than the Rossby deformation length of order 100 kilometer and longer than outer turbulence scales of order one meter do not have a well-established theoretical underpinning because of the paucity of observational constraints. At scales shorter than the Rossby length scale, quasigeostrophic (QG) theory predicts that tracers should have a spectrum of slope of minus one [corresponding to tracer-gradient spectra with slope plus one]. This contrasts with numerous observations spanning the horizontal horizontal wavelengths 30 m to 500 km which report significantly redder and often almost flat tracer-gradient spectra over this wavenumber band. Similar dynamical comparisons are in short supply. High resolution sections of the upper 150 meter of the ocean will be sampled using a towed chain with tightly spaced temperature, conductivity and pressure (CTD) sensors and the shipboard Acoustic Doppler Current Profiler (ADCP). This project will characterize the horizontal wavenumber spectra of passive tracers (water-mass, spice, salinity anomalies) on isopycnals to higher horizontal wavenumbers than previously accomplished, and resolve the sub-inertial O(1 km) horizontal strain tensor thought responsible for stirring on these scales, as well as determine strain timescales. These measurements will provide key observational constraints on order one Rossby number and Richardson number flows.