Study of ageostrophy during strong, nonlinear eddy-front interaction in the Gulf of Mexico
Study of ageostrophy during strong, nonlinear eddy-front interaction in the Gulf of Mexico
复制标题
在墨西哥湾强非线性涡锋相互作用期间非地转的研究
DOI：
10.1175/jpo-d-20-0182.1
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发表时间：
2021-03
影响因子：
3.5
通讯作者：
L. Hiron;D. Nolan;L. Shay
中科院分区：
文献类型：
--
作者：
L. Hiron;D. Nolan;L. Shay
中尺度涡旋驱动了海洋中很大一部分的变化。与其平移速度相比，具有较强切向速度的涡流能够保持连贯性并进行长距离旅行，携带海洋周围的水质量特性，热量，营养物质和颗粒。这些中尺度特征的非线性是更强的流动和更大的曲率，因此，与更大的离心力。墨西哥湾环流（LC）系统长期以来一直被认为是接近地转平衡，尽管其强大的流动和发展的大曲折和强锋涡在不稳定的阶段。LC曲折和它的锋面涡之间的区域被证明有高的Rossby数表示非线性，然而，非线性项的影响上的流动还没有被研究到目前为止。在这项研究中，非地转的LC曲流进行了评估，使用高分辨率的数值模式和地转速度测高。本研究所用的方法可适用于任何离心力重要的区域。结果表明，在强弯曲过程中，特别是在LC脱落前和脱落过程中以及存在锋面涡时，离心力与科里奥利力和压力梯度力一样重要，LC弯曲处于梯度风平衡状态。离心力调制的平衡和修改的流速，导致在LC曲流槽的亚地转流在LC曲流波峰的锋面涡和超地转流周围。当修正测高的地转速度以考虑离心力时，也发现了同样的模式。在模式中，气旋性和反气旋性曲流的非地转百分比分别为47% 1%和78%8%，在测高数据集中，分别为31%3%和78%29%。因此，非地转速度是LC流的一个重要分量，在研究LC系统时不可忽略。一百六十;  
Mesoscale eddies drive a large fraction of the variability in the ocean. Eddies with strong tangential velocity compared to their translation speed are able to stay coherent and travel long distances, carrying water mass properties, heat, nutrients, and particles around the ocean. The nonlinearity of these mesoscale features is greater for stronger flow and greater curvature, which, consequently, is associated with greater centrifugal force.The Gulf of Mexico Loop Current (LC) system has long been assumed to be close to geostrophic balance despite its strong flow and the development of large meanders and strong frontal eddies during unstable phases. The region between the LC meanders and its frontal eddies was shown to have high Rossby numbers indicating nonlinearity; however, the effect of the nonlinear term on the flow has not been studied so far. In this study, the ageostrophy of the LC meanders is assessed using a high-resolution numerical model and geostrophic velocities from altimetry. The method used in this study can be applied in any region where the centrifugal force is important. A formula to compute the radius of curvature of the flow from the velocity field is also presented.The results indicate that during strong meandering, especially before and during LC shedding and in the presence of frontal eddies, the centrifugal force becomes as important as the Coriolis force and the pressure-gradient force: LC meanders are in gradient-wind balance. The centrifugal force modulates the balance and modifies the flow speed, resulting in a subgeostrophic flow in the LC meander trough around the frontal eddies and supergeostrophic flow in the LC meander crest. The same pattern is found when correcting the geostrophic velocities from altimetry to account for the centrifugal force. The ageostrophic percentage in the cyclonic and anticyclonic meanders is 47% ± 1% and 78% ± 8% in the model and 31% ± 3% and 78% ± 29% in the altimetry dataset, respectively. Thus, the ageostrophic velocity is an important component of the LC flow and cannot be neglected when studying the LC system.