Vertical wave number spectra of velocity and shear at small internal wave scales
Vertical wave number spectra of velocity and shear at small internal wave scales
复制标题
小内波尺度下速度和剪切的垂直波数谱
DOI：
--
复制
发表时间：
1989
期刊：
影响因子：
--
通讯作者：
C. Cox
中科院分区：
文献类型：
--
作者：
T. Duda;C. Cox
我们分析了从五套每小时垂直剖面上的海洋水平速度与笛卡尔潜水员速度记录仪收集的频谱。每组包括11至27个剖面，深度范围为25-220米至25-340米。在[0.02-0.1] cpm波段，速度和剪切的垂直波数（m）功率谱没有可再现的幂律形式。剪切谱随波数的增加先上升后下降，过渡波数mc在上述范围内变化。对于剪切谱，在0.1 cpm附近的m处的陡度范围为m−1/2至m−2。数据集分为两类。对于一个群，逆理查森函数Ri−1（mc）的值接近2。尽管速度变化是可变的，但这些集合的Ri−1（0.1 cpm）为1.3，表明剪切接近饱和。Ri−1（0.l）的低变率，尽管这一群的动能变率很高，这表明高波数的能量（以及切变）被抑制了。这表明不稳定机制在高波数下衰减光谱，衰减变得更宽，并在较高能量下逐渐影响较低的垂直波数（除了一贯受影响的高波数）。对于另一组，Ri−1（0.1）<$1，剪切谱不太陡峭，剪切集中在高波数处，这表明在我们测量带的小尺度端衰减较小。对于这两个群体，预测波数的频谱陡峭，估计从数据使用两种技术，与水平动能带[0.005-0.01] cpm，量化剪切频谱滚降近似成反比。
We analyze spectra from five sets of hourly vertical profiles of upper-ocean horizontal velocity collected with the Cartesian Diver velocity recorder. Each set consists of 11 to 27 profiles over depth ranges of 25–220 m to 25–340 m. The vertical wave number (m) power spectra of velocity and shear have no reproducible power law form in the band [0.02–0.1] cpm. Shear spectra tend to rise then fall with increasing wave number, with the transition wave number mc varying within the above band. For shear spectra, steepness at m near 0.1 cpm ranges from m−1/2 to m−2. The data sets fall into two categories. For one group, inverse Richardson functions Ri−1(mc) have values near 2. Despite variability of velocity variance, these sets have Ri−1(0.1 cpm) ≈ 3, suggesting that shear is near saturation. Low variability of Ri−1(0.l), despite high kinetic energy variability for this group, suggests that energy at high wave number (and thus shear) is suppressed. This suggests that instability mechanisms attenuate spectra at high wave number, with attenuation becoming more broadband and influencing progressively lower vertical wave numbers (in addition to consistently influenced high wave numbers) at higher energy. For the other group, Ri−1(0.1) ≈ 1, shear spectra are less steep, and shear is concentrated at high wave number, suggesting less attenuation at the small-scale end of our measurement band. For both groups, predicted wave numbers of spectral steepening, estimated from the data using two techniques, are related approximately inversely with horizontal kinetic energy in the band [0.005–0.01] cpm, quantifying the shear spectral roll-off.