Impact of hydrographic data assimilation on the modelled Atlantic meridional overturning circulation
Impact of hydrographic data assimilation on the modelled Atlantic meridional overturning circulation
复制标题
水文数据同化对模拟大西洋经向翻转环流的影响
DOI：
10.5194/os-6-761-2010
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发表时间：
2009
期刊：
影响因子：
3.2
通讯作者：
S. Cunningham
中科院分区：
文献类型：
--
作者：
Gregory C. Smith;K. Haines;T. Kanzow;S. Cunningham
抽象的。在这里，我们朝着海洋同化系统的发展迈出了第一步，该系统可以限制模拟的大西洋经向翻转环流（AMOC），以支持气候预测。详细比较了1°和1/4°分辨率的全球模式模拟（有和没有顺序数据同化）与大西洋26.5° N的RAPID系泊阵列的观测和输运估计。从合并的RAPID边界阵列的观测模拟水的属性的比较表明，在原位数据同化的能力，以准确地约束这些系泊阵列之间的东西向密度梯度。然而，当同化原位数据时，阿巴科岛和快速系泊点WB 2（离岸16 km）之间存在不受约束的“西部边界楔”，导致该区域错误的南向流加剧。其结果是，与从RAPID阵列得出的估计相比，向南的中上层海洋迁移（0- 1 100米）过于强烈。上层纬向密度梯度的校正被发现，以弥补主要是一个弱的副热带涡旋环流在自由模式运行（即没有同化）。尽管同化对上层的密度结构和输送产生了重要的变化，但AMOC的振幅和亚季节变率的变化很小。这表明上层密度信息的同化主要投射在涡旋环流上，而对26° N的AMOC影响很小，这是由于缺乏对Argo最大深度（2000 m）以下密度梯度的修正。初始条件的敏感性进行了探讨，通过两个额外的实验，使用气候的初始条件。这些实验表明，在控制模拟（没有数据同化）的环流强度的弱偏差的发展在一段时间内约6个月，但这样做独立于翻转，没有变化的AMOC。然而，在北大西洋深水（NADW）的属性和体积运输的差异持续整个3年的模拟结果在AMOC强度的差异为3西弗。这些密集的水异常的持续性和它们对AMOC的影响是有希望的十年期预报能力的发展。结果表明，更深的沃茨必须准确地再现，以限制AMOC。
Abstract. Here we make an initial step toward the development of an ocean assimilation system that can constrain the modelled Atlantic Meridional Overturning Circulation (AMOC) to support climate predictions. A detailed comparison is presented of 1° and 1/4° resolution global model simulations with and without sequential data assimilation, to the observations and transport estimates from the RAPID mooring array across 26.5° N in the Atlantic. Comparisons of modelled water properties with the observations from the merged RAPID boundary arrays demonstrate the ability of in situ data assimilation to accurately constrain the east-west density gradient between these mooring arrays. However, the presence of an unconstrained "western boundary wedge" between Abaco Island and the RAPID mooring site WB2 (16 km offshore) leads to the intensification of an erroneous southwards flow in this region when in situ data are assimilated. The result is an overly intense southward upper mid-ocean transport (0–1100 m) as compared to the estimates derived from the RAPID array. Correction of upper layer zonal density gradients is found to compensate mostly for a weak subtropical gyre circulation in the free model run (i.e. with no assimilation). Despite the important changes to the density structure and transports in the upper layer imposed by the assimilation, very little change is found in the amplitude and sub-seasonal variability of the AMOC. This shows that assimilation of upper layer density information projects mainly on the gyre circulation with little effect on the AMOC at 26° N due to the absence of corrections to density gradients below 2000 m (the maximum depth of Argo). The sensitivity to initial conditions was explored through two additional experiments using a climatological initial condition. These experiments showed that the weak bias in gyre intensity in the control simulation (without data assimilation) develops over a period of about 6 months, but does so independently from the overturning, with no change to the AMOC. However, differences in the properties and volume transport of North Atlantic Deep Water (NADW) persisted throughout the 3 year simulations resulting in a difference of 3 Sv in AMOC intensity. The persistence of these dense water anomalies and their influence on the AMOC is promising for the development of decadal forecasting capabilities. The results suggest that the deeper waters must be accurately reproduced in order to constrain the AMOC.