Submesoscale Frontal Instabilities Modulate Large‐Scale Distribution of the Winter Deep Mixed Layer in the Kuroshio‐Oyashio Extension
Submesoscale Frontal Instabilities Modulate Large‐Scale Distribution of the Winter Deep Mixed Layer in the Kuroshio‐Oyashio Extension
复制标题
亚中尺度锋面不稳定性调节黑潮-亲潮延伸区冬季深层混合层的大规模分布
DOI：
10.1029/2022jc018915
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
Zhang Yang
中科院分区：
文献类型：
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作者：
Ding Yang;Xu Lixiao;Xie Shang‐Ping;Sasaki Hideharu;Zhang Zhengguang;Cao Haijin;Zhang Yang
在中纬度北太平洋，黑潮-Oyashio延伸(KOE)区冬季海洋热损失最大。然而，那里的混合层深度(MLD)是浅的(<；50m)，两侧是一条深MLD(>；100m)的带状带。这种观测到的混合层模式不能用粗分辨率或中尺度涡旋分辨率(1/10°)模式再现。是什么导致了观测到的沿Koe锋区的MLD浅滩？结果表明，1/30°亚中尺度海洋环流模式很好地再现了锋面混合层浅化现象，表明它与亚中尺度锋面动力学密切相关。沿锋面的地转应变率较大，有利于亚中尺度锋面不稳定。冬季表面浮力的损失减少了层结，并增强了锋面(即，向北上升的陡峭等轴线)。储存在窄锋面的有效势能可以通过混合层斜压不稳定(MLI)以涡动动能的形式释放出来。与MLI相关的剧烈的非地转运动有效地使垂直方向的等地轴线塌陷，并使混合层重新分层。因此，尽管冬季有很强的地表热量损失和风的搅动，但KOE锋区的MLD是浅的。这里揭示的亚中尺度过程对于改进气候模式具有重要的意义。
In the mid‐latitude North Pacific, the wintertime ocean heat loss reaches the maximum in the Kuroshio‐Oyashio Extension (KOE) region. However, the mixed layer depth (MLD) there is shallow (<50 m), flanked by a zonal band of deep MLD (>100 m) on either side. Such an observed mixed layer pattern is not reproduced by coarse‐resolution or mesoscale eddy‐resolving (1/10°) models. What causes the observed MLD shoaling along the KOE frontal region? Here we show that the mixed layer shoaling in the front is well reproduced by a 1/30°, submesoscale‐permitting ocean general circulation model, indicating that it is closely related to the submesoscale frontal dynamics. The geostrophic strain rate is strong along the sharp KOE front, favoring submesoscale frontal instabilities. The surface buoyancy loss during winter reduces stratification and enhances the fronts (i.e., with steeper, northward rising isopycnals). The available potential energy stored in the narrow fronts can be released in the form of eddy kinetic energy by the mixed layer baroclinic instabilities (MLI). The associated vigorous ageostrophic motions associated with MLI efficiently slump the vertically oriented isopycnals and restratify the mixed layer. Thus, the MLD is shallow in the KOE frontal region despite the strong surface heat loss and wind stirring during winter. The submesoscale processes revealed here have important implications for improving climate models.