Submesoscale Coherent Structures on the Continental Shelf
Submesoscale Coherent Structures on the Continental Shelf
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DOI：
10.1175/jpo-d-16-0270.1
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发表时间：
2017-12-01
影响因子：
3.5
通讯作者：
Uchiyama, Yusuke
中科院分区：
文献类型：
--
作者：
Dauhajre, Daniel P.;McWilliams, James C.;Uchiyama, Yusuke
通过对南加州湾（SCB）进行高分辨率（Delta x = 75 m）区域海洋模拟系统（ROMS）模拟，可以发现和分析大陆架上O（0.3-30）km的次中尺度变率。这种可变性表现在无处不在但短暂的相干结构中：锋、细丝和涡旋。类似于他们的开放的海洋同行，在大陆架上的锋和细丝确定其强大的垂直速度，表面辐合，气旋涡度和水平密度梯度。这些特征的生命周期通常持续3-5天，其中地层由增加密度和速度梯度的水平平流趋势主导（即，锋生）。海岸线的形状和水柱的深度都影响浅水锋和细丝的丰度和空间方向。在靠近海岸的地方，锋面和丝状体常常与等深线平行排列，海岬常常是通过底应力产生强烈涡度的场所。旋转、气压梯度和垂直混合之间的准定常、近似动量平衡--被称为湍流热成风（TTW）--通常在锋面和细丝附近的强次级环流中有效。然而，锋和花丝环流受地面加热和垂直混合强烈的日变化是不一致的稳态TTW平衡。二次环流可以诱导短暂的物质捕获和大陆架上的大量垂直热通量。
Discovery and analysis of submesoscale variability O(0.3-30) km on the continental shelf is made possible by a high-resolution (Delta x = 75 m) Regional Oceanic Modeling System (ROMS) simulation of the Southern California Bight (SCB). This variability is manifest in ubiquitous yet ephemeral coherent structures: fronts, filaments, and vortices. Similar to their open-ocean counterparts, fronts and filaments on the shelf are identified by their strong vertical velocity, surface convergence, cyclonic vorticity, and horizontal density gradient. Life cycles of these features typically last 3-5 days, with the formation dominated by a horizontal advective tendency that increases density and velocity gradients (i.e., frontogenesis). The shape of the coastline and depth of the water column both influence the abundance and spatial orientation of shallow-water fronts and filaments. Closer to shore, fronts and filaments often align themselves parallel to isobaths, and headlands often act as sites of intense vorticity generation through bottom stress. A quasi-steady, approximate momentum balance among rotation, pressure gradient, and vertical mixing-known as turbulent thermal wind (TTW)-often is valid in the strong secondary circulations local to fronts and filaments. However, front and filament circulations subject to strong diurnal variation in surface heating and vertical mixing are inconsistent with steady-state TTW balance. The secondary circulations can induce ephemeral material trapping and substantial vertical heat fluxes on the shelf.