Topographic Influence on Baroclinic Instability and the Mesoscale Eddy Field in the Northern North Atlantic Ocean and the Nordic Seas
Topographic Influence on Baroclinic Instability and the Mesoscale Eddy Field in the Northern North Atlantic Ocean and the Nordic Seas
复制标题
地形对北大西洋北部和北欧海域斜压不稳定性和中尺度涡流场的影响
DOI：
10.1175/jpo-d-17-0220.1
复制
发表时间：
2018
影响因子：
3.5
通讯作者：
P. Isachsen
中科院分区：
文献类型：
--
作者：
M. Trodahl;P. Isachsen
在北大西洋北方和北欧海域，行星涡度梯度和密度层结较弱，导致时间平均海流受到海底地形的强烈引导。地形转向建立了明显的边界流与强大的财产前，倾向于斜压和正压不稳定。这些不稳定的过程产生了一个宏观湍流涡流场，扩散浮力和其他示踪剂从边界电流和深盆地。在本文中，我们调查的斜压不稳定性所发挥的特殊作用，在产生所观察到的涡流场，比较预测的线性稳定性计算诊断从非线性涡流允许的海洋模型后报。我们还研究了海底地形如何影响不稳定性本身。计算结果表明，斜压不稳定是一个一致的涡动场的来源，但地形位涡梯度影响不稳定的增长显着。我们还观察到系统的地形效应的有限振幅涡特征，包括一般抑制的长度尺度的大陆坡。不稳定模式的垂直结构的调查表明，Eady理论，即使修改到考虑底坡，是不适合作为一个最低阶的动态发生在这些海洋区域的模型。
A weak planetary vorticity gradient and weak density stratification in the northern North Atlantic and Nordic seas lead to time-mean currents that are strongly guided by bottom topography. The topographic steering sets up distinct boundary currents with strong property fronts that are prone to both baroclinic and barotropic instability. These instability processes generate a macroturbulent eddy field that spreads buoyancy and other tracers out from the boundary currents and into the deep basins. In this paper we investigate the particular role played by baroclinic instability in generating the observed eddy field, comparing predictions from linear stability calculations with diagnostics from a nonlinear eddy-permitting ocean model hindcast. We also look into how the bottom topography impacts instability itself. The calculations suggest that baroclinic instability is a consistent source of the eddy field but that topographic potential vorticity gradients impact unstable growth significantly. We also observe systematic topographic effects on finite-amplitude eddy characteristics, including a general suppression of length scales over the continental slopes. Investigation of the vertical structure of unstable modes reveal that Eady theory, even when modified to account for a bottom slope, is unfit as a lowest-order model for the dynamics taking place in these ocean regions.