Vertical Fluxes Conditioned on Vorticity and Strain Reveal Submesoscale Ventilation
Vertical Fluxes Conditioned on Vorticity and Strain Reveal Submesoscale Ventilation
复制标题
DOI：
10.1175/jpo-d-21-0016.1
复制
发表时间：
2021-09-01
影响因子：
3.5
通讯作者：
Gray, Alison R.
中科院分区：
文献类型：
--
作者：
Balwada, Dhruv;Xiao, Qiyu;Gray, Alison R.
据推测，由于亚中尺度流具有很强的相关垂直速度，因此在气候重要示踪剂的垂直输送中起着重要作用。然而，输运的多尺度、非线性和拉格朗日性质使得将示踪剂通量的比例归因于某些过程、尺度、区域或特征具有挑战性。基于表面涡度和应变联合概率分布函数（JPDF）的判据有效地将表面速度场分解为可区分的流动区域，不同的流动区域包含不同的流动特征，如锋面或涡流。JPDF具有独特的形状，并且近似地将流解析为不同的尺度，因为较大的速度梯度通常与较小的尺度相关联。因此，调节垂直示踪剂在涡度-应变JPDF上的输送有助于将输送归因于不同类型的流动和尺度。应用于一组理想化的南极环极流模拟（仅在水平分辨率上有所不同），这种诊断方法表明，通常与亚中尺度锋面相关的小规模应变主导区域，尽管其空间足迹很小，但在混合层基底交换示踪剂方面发挥了巨大的作用，并且是大规模示踪剂预算的重要贡献者。解决这些流动不仅在小尺度上增加了额外的通量，而且由于更大尺度的流动而增加了通量。
It has been hypothesized that submesoscale flows play an important role in the vertical transport of climatically important tracers, due to their strong associated vertical velocities. However, the multiscale, nonlinear, and Lagrangian nature of transport makes it challenging to attribute proportions of the tracer fluxes to certain processes, scales, regions, or features. Here we show that criteria based on the surface vorticity and strain joint probability distribution function (JPDF) effectively decompose the surface velocity field into distinguishable flow regions, and different flow features, like fronts or eddies, are contained in different flow regions. The JPDF has a distinct shape and approximately parses the flow into different scales, as stronger velocity gradients are usually associated with smaller scales. Conditioning the vertical tracer transport on the vorticity-strain JPDF can therefore help to attribute the transport to different types of flows and scales. Applied to a set of idealized Antarctic Circumpolar Current simulations that vary only in horizontal resolution, this diagnostic approach demonstrates that small-scale strain-dominated regions that are generally associated with submesoscale fronts, despite their minuscule spatial footprint, play an outsized role in exchanging tracers across the mixed layer base and are an important contributor to the large-scale tracer budgets. Resolving these flows not only adds extra flux at the small scales, but also enhances the flux due to the larger-scale flows.