The Regeneration of the Lofoten Vortex through Vertical Alignment
The Regeneration of the Lofoten Vortex through Vertical Alignment
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DOI：
10.1175/jpo-d-20-0029.1
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发表时间：
2020-09
影响因子：
3.5
通讯作者：
M. Trodahl;P. Isachsen;J. Lilly;J. Nilsson;N. Kristensen
中科院分区：
文献类型：
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作者：
M. Trodahl;P. Isachsen;J. Lilly;J. Nilsson;N. Kristensen
过去几十年的观测促进了罗弗敦盆地存在一个长期存在的反气旋涡旋的观点。尽管多次记录到强烈的反气旋，但观测结果并不能确定这个特征是一个单一的涡旋还是一连串短暂的涡旋。一个持续数十年的漩涡需要某种重振机制。冬季对流和涡旋合并已被提出候选。我们使用高分辨率区域海洋模型研究罗浮敦盆地涡旋动力学。该模型从一个较粗的弱涡场初始化。坡流加强并释放反气旋涡流，这些涡流漂移到盆地。半年后，一个反气旋到达中心，为整个模拟过程中保持清晰的漩涡提供核心。分析表明，该涡旋是由较轻的反气旋的反复吸收和垂直堆积形成的。这压缩并与潜在涡量守恒相一致，强化了组合涡，使其变得更加垂直分层，并在此过程中排出一些流体。冬季对流的作用主要是使涡旋在垂直方向上均匀化和致密化，而不是增强它。此外，从大陆坡上脱落的反气旋的地形导向对罗浮敦涡旋的存在和恢复至关重要。这些结果为研究海洋反气旋的再生提供了新的视角。在这种情况下，罗浮敦漩涡通过重复的合并事件得以维持。流体仍然是逐渐交换的，虽然旋涡是可识别的持续极值的潜在涡度。
Observations from the past decades have promoted the idea of a long-lived anticyclonic vortex residing in the Lofoten Basin. Despite repeatedly recorded intense anticyclones, the observations cannot firmly decide whether the signature is of a single vortex or a succession of ephemeral vortices. A vortex persisting for decades requires some reinvigoration mechanism. Wintertime convection and vortex merging have been proposed candidates. We examine Lofoten Basin vortex dynamics using a high-resolution regional ocean model. The model is initialized from a coarser state with a weak eddy field. The slope current intensifies and sheds anticyclonic eddies that drift into the basin. After half a year, an anticyclone arrives at the center, providing the nucleus for a vortex that remains distinct throughout the simulation. Analyses show that this vortex is regenerated by repeated absorption and vertical stacking of lighter anticyclones. This compresses and—in concert with potential vorticity conservation—intensifies the combined vortex, which becomes more vertically stratified and also expels some fluid in the process. Wintertime convection serves mainly to vertically homogenize and densify the vortex, rather than intensifying it. Further, topographic guiding of anticyclones shed from the continental slope is vital for the existence and reinvigoration of the Lofoten vortex. These results offer a new perspective on the regeneration of oceanic anticyclones. In this scenario the Lofoten vortex is maintained through repeated merging events. Fluid remains gradually exchanged, although the vortex is identifiable as a persistent extremum in potential vorticity.