Anomalies of meridional overturning:: Mechanisms in the North Atlantic
Anomalies of meridional overturning:: Mechanisms in the North Atlantic
复制标题
DOI：
10.1175/jpo2767.1
复制
发表时间：
2005-08-01
影响因子：
3.5
通讯作者：
Köhl, A
中科院分区：
文献类型：
--
作者：
Köhl, A
利用最佳观测资料研究了北大西洋北纬30度、深度900米的翻转流函数。这些观测的目的是在同化时最大限度地影响数值模式中的经向翻转环流，从而建立最有效的观测网络来研究经圈翻转环流的变化。它们也非常适合于研究大气环流模型中的相关物理机制。最佳观测值在全球1度模式的框架内进行了评估，时间跨度为10年。对监测MOC有用的水文观测主要位于北纬30度以北的西部边界和北纬30度以南的东部边界。其他地点还包括拉布拉多、伊明格和伊比利亚海。在不到一年的时间尺度上，MOC的变化主要是由风驱动的，并通过Ekman输送和沿海升降流的变化来弥补。只有一小部分是浮力驱动的，在几年的时间尺度上对拉布拉多海和伊明格海的冬季异常做出了缓慢的反应。这些异常通过拉布拉多海水深度处的内部开尔文波沿西海岸向南传播。他们主要把条件设在MOC异常的北缘。南缘主要是由加那利盆地温度和盐度异常引起的平流型Rossby波变化。这些异常在副热带环流的斜压不稳定区域向西传播时被放大。因此，最大MOC响应的确切经向位置由这两个信号的强度之比确定。
Optimal observations are used to investigate the overturning streamfunction in the North Atlantic at 30 degrees N and 900-m depth. Those observations are designed to impact the meridional overturning circulation (MOC) in numerical models maximally when assimilated and therefore establish the most efficient observation network for studying changes in the MOC. They are also ideally suited for studying the related physical mechanisms in a general circulation model. Optimal observations are evaluated here in the framework of a global 1 degrees model over a 10-yr period. Hydrographic observations useful to monitor the MOC are primarily located along the western boundary north of 30 degrees N and along the eastern boundary south of 30 degrees N. Additional locations are in the Labrador, Irminger, and Iberian Seas. On time scales of less than a year, variations in MOC are mainly wind driven and are made up through changes in Ekman transport and coastal up- and downwelling. Only a small fraction is buoyancy driven and constitutes a slow response, acting on time scales of a few years, to primarily wintertime anomalies in the Labrador and Irminger Seas. Those anomalies are communicated southward along the west coast by internal Kelvin waves at the depth level of Labrador Sea Water. They primarily set the conditions at the northern edge of the MOC anomaly. The southern edge is mainly altered through Rossby waves of the advective type, which originate from temperature and salinity anomalies in the Canary Basin. Those anomalies are amplified on their way westward in the baroclinic unstable region of the subtropical gyre. The exact meridional location of the maximum MOC response is therefore set by the ratio of the strength of these two signals.