Where Does Dense Water Sink? A Subpolar Gyre Example*
Where Does Dense Water Sink? A Subpolar Gyre Example*
复制标题
浓水会沉到哪里？
DOI：
10.1175/1520-0485(2001)031
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发表时间：
2001
影响因子：
3.5
通讯作者：
R. Pickart
中科院分区：
文献类型：
--
作者：
M. Spall;R. Pickart
研究认为，温盐环流下沉支流的主要成分发生在靠近陡峭地形的对流混合区域。给出了这种边界对流所产生的倾覆力的一个简单的理论估计，它仅取决于沿边界的海洋混合层的性质。比例尺估计表明，边界对流造成的下沉比由大尺度动力学或深层对流场地的斜压不稳定造成的公海下沉大一个数量级。拉布拉多海最近的水文观测被用来估计由于这些不同的机制而产生的下沉，并支持边界下沉占主导地位的观点。该理论与非涡旋分辨大气环流模型在大范围参数范围内诊断的倾覆率进行了很好的比较。作为这些动力的直接结果，模式中的高纬度水文和翻转环流对气旋边缘流的存在非常敏感。环流在亚极涡中的横向密度平流增加了层结，限制了边界附近的混合，从而减少了最大下沉。结果表明，高纬经向热量输送主要是水平环流输送，而不是翻转环流输送。这种边缘流存在于模式的不同构型中，包括1)大陆斜率和标准扩散参数，以及2)零水平扩散和平底。
It is proposed that a dominant component of the downwelling limb of the thermohaline circulation takes place in regions where convective mixing is found adjacent to steep topography. A simple theoretical estimate of the overturning forced by such boundary convection is derived that depends only on the properties of the oceanic mixed layer along the boundary. Scaling estimates indicate that sinking forced by boundary convection is an order of magnitude greater than sinking in the open ocean resulting from large-scale dynamics or baroclinic instability of deep convective sites. Recent hydrographic observations in the Labrador Sea are used to estimate the downwelling due to these different mechanisms and support the notion that boundary sinking dominates. The theory compares well with the overturning rates diagnosed in a noneddy-resolving general circulation model over a wide range of parameters. As a direct consequence of these dynamics, the high-latitude hydrography and overturning circulation in the model are very sensitive to the presence of cyclonic rim currents. Lateral density advection by the rim currents in the subpolar gyre increases the stratification and limits the mixing near the boundaries, thus reducing the maximum downwelling. As a result, most of the high-latitude meridional heat transport is carried by the horizontal circulation instead of the overturning circulation. Such rim currents are found in different configurations of the model, including 1) a continental slope and standard diffusion parameters and 2) zero horizontal diffusion and a flat bottom.