Mixed layer depth front and subduction of low potential vorticity water in an idealized ocean GCM
Mixed layer depth front and subduction of low potential vorticity water in an idealized ocean GCM
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DOI：
10.1007/s10872-007-0010-0
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发表时间：
2007-02
影响因子：
2.3
通讯作者：
Shiro Nishikawa;Atsushi Kubokawa
中科院分区：
文献类型：
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作者：
Shiro Nishikawa;Atsushi Kubokawa
在副热带环流的混合层深度（MLD）分布上存在一个锋面状结构，称为MLD锋面，它与模态水的形成区有关。本文利用一个不考虑季节强迫的理想海洋环流模式，研究了MLD锋的形成机制。首先证明了MLD锋沿着一条满足ug·Tts = 0的曲线出现（ug是上层海洋地转速度矢量，Tts是海表温度，Tts是水平梯度算子）。也就是说，锋面是俯冲区域（ug·WITTs> 0）和未发生俯冲的区域（ug·WITTs < 0）之间的边界。其次，我们研究了MLD锋面上的低位涡水的俯冲，这是过去的研究所指出的。由于MLD前缘处的Et = 0，水粒子不会穿过MLD前缘处的露头。在MLD锋面俯冲的水来自海表温度高于MLD锋面的深混合层区域。深混合层区的水温随平流向东降低，在MLD锋处达到最低值，此时ug·mTs = 0，然后潜到较暖的近地层之下。由于深层混合层水在薄的分层表层下俯冲，保持其厚度，混合层深度在俯冲位置突然变化。
It is known that there is a front-like structure at the mixed layer depth (MLD) distribution in the subtropical gyre, which is called the MLD front, and is associated with the formation region of mode water. In the present article, the generation mechanism of the MLD front is studied using an idealized ocean general circulation model with no seasonal forcing. First, it is shown that the MLD front occurs along a curve whereug·∇Ts= 0 is satisfied (ugis the upper ocean geostrophic velocity vector,Tsis the sea surface temperature and ∇ is the horizontal gradient operator). In other words, the front is the boundary between the subduction region (ug·∇Ts> 0) and the region where subduction does not occur (ug·∇Ts< 0). Second, we have investigated subduction of low potential vorticity water at the MLD front, which has been pointed out by past studies. Sinceug·∇Ts= 0 at the MLD front, the water particles do not cross the outcrop at the MLD front. The water that is subducted at the MLD front has come from the deep mixed layer region where the sea surface temperature is higher than that at the MLD front. The temperature of the water in the deep mixed layer region decreases as it is advected eastward, attains its minimum at the MLD front whereug·∇Ts= 0, and then subducts under the warmer surface layer. Since the deep mixed layer water subducts beneath a thin stratified surface layer, maintaining its thickness, the mixed layer depth changes abruptly at the subduction location.