Ertel Potential Vorticity versus Bernoulli Potential on Approximately Neutral Surfaces in the Antarctic Circumpolar Current
Ertel Potential Vorticity versus Bernoulli Potential on Approximately Neutral Surfaces in the Antarctic Circumpolar Current
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南极绕极流中近似中性表面上的埃特尔位涡度与伯努利势的关系
DOI：
10.1175/jpo-d-19-0140.1
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发表时间：
2020
影响因子：
3.5
通讯作者：
Stanley G
中科院分区：
文献类型：
--
作者：
Stanley G
利用南大洋状态估计，研究了南极绕极流（ACC）中Ertel位涡Q和Bernoulli位涡B在正压密度面上的关系.类似于地球和火星的大气层外，Q和B在ACC中以类似函数的方式相互关联，并具有适度的散射。在近表面之下，与Q和B相关的基本函数似乎是近似线性的。无量纲化其斜率产生“Ma”，即长Rossby波的“马赫”数，即局部流速与固有长Rossby波速度的比值。我们经验估计后者使用既定的和新的技术，产生定性一致的结果。以前的工作将“Ma”与Q的均匀性程度和Arnol'd的剪切稳定性标准联系起来。在所研究的所有绕极浮力表面上，整个ACC的“Ma”估计值都是显著正的，这意味着不可忽略的Q。上层一般表现出“马”略小于单位，这表明剪切不稳定可能在这些层内运作。深层显示“马”大于统一，意味着稳定。在浅于1000米的表面上的ACC北部，QversusBslope变化强烈的亚年度和年际的时间尺度，但“马”徘徊在统一附近。我们还研究了空间变异性：ACC上点缀着数百个小尺度特征，“Ma”接近统一，而远离ACC的“Ma”更常见的是负的或高于统一，两者都对应于稳定性。时间平均“Ma”的地图显示，稳定区域占据了南大洋的大部分地区，除了几个地形控制的热点地区，“Ma”总是接近统一。
We investigate the relationship between Ertel potential vorticityQand Bernoulli potentialBon orthobaric density surfaces in the Antarctic Circumpolar Current (ACC), using the Southern Ocean State Estimate. Similar to the extratropical atmospheres of Earth and Mars,QandBcorrelate in the ACC in a function-like manner with modest scatter. Below the near-surface, the underlying function relatingQandBappears to be nearly linear. Nondimensionalizing its slope yields “Ma,” a “Mach” number for long Rossby waves, the ratio of the local flow speed to the intrinsic long Rossby wave speed. We empirically estimate the latter using established and novel techniques that yield qualitatively consistent results. Previous work related “Ma” to the degree of homogeneity ofQand to Arnol’d’s shear stability criteria. Estimates of “Ma” for the whole ACC are notably positive, implying inhomogeneousQ, on all circumpolar buoyancy surfaces studied. Upper layers generally exhibit “Ma” slightly less than unity, suggesting that shear instability may operate within these layers. Deep layers exhibit “Ma” greater than unity, implying stability. On surfaces shallower than 1000 m just north of the ACC, theQversusBslope varies strongly on subannual and interannual time scales, but “Ma” hovers near unity. We also study spatial variability: the ACC is speckled with hundreds of small-scale features with “Ma” near unity, whereas away from the ACC “Ma” is more commonly negative or above unity, both corresponding to stability. Maps of the time-mean “Ma” show stable regions occupy most of the Southern Ocean, except for several topographically controlled hotspots where “Ma” is always near unity.
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