The contribution of eastern-boundary density variations to the Atlantic meridional overturning circulation at 26.5° N
The contribution of eastern-boundary density variations to the Atlantic meridional overturning circulation at 26.5° N
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DOI：
10.5194/os-6-475-2010
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发表时间：
2010-01-01
期刊：
影响因子：
3.2
通讯作者：
Marotzke, J.
中科院分区：
文献类型：
--
作者：
Chidichimo, M. P.;Kanzow, T.;Marotzke, J.
我们研究东边界密度变化的贡献，亚季节和季节异常的强度和垂直结构的大西洋经向翻转环流（AMOC）在26.5度N，通过快速/MOCHA系泊阵列2004年4月和2007年10月之间。主要的密度异常出现在500 m以上，1400 m以下的密度异常往往是一致的。密度有13天的波动，这是明显的下降到3500米。测量东边界密度的两种策略-高离岸系泊（EB 1）和大陆坡（EBH）上的系泊阵列-在幅度、垂直结构和由此产生的全流域综合输运波动的频率分布方面几乎没有对应关系，这意味着EB 1和EBH之间有显著的输运贡献。与最初的计划相反，EB 1的测量结果不能作为EBH的备份或替代：密度需要直接在大陆坡测量，以计算整个流域的密度梯度。EBH的密度波动在AMOC中产生2 Sv rms的运输可变性，而总体AMOC可变性为4.8 Sv rms。东部边界的密度有明显的季节性变化，在100 ~ 1400 m之间变化明显，春季正异常最大，秋季负异常最大。这些变化在春季驱动异常的南向上层中层洋流，这意味着AMOC的最大减少，反之亦然，在秋季。东边界密度引起的AMOC的季节性周期的振幅为5.2 Sv峰到峰，占主导地位的6.7 Sv峰到峰的总AMOC的季节性周期。我们的分析表明，密度的季节性周期可能是由风应力旋度的强近海岸季节性周期所强迫的。
We study the contribution of eastern-boundary density variations to sub-seasonal and seasonal anomalies of the strength and vertical structure of the Atlantic Meridional Overturning Circulation (AMOC) at 26.5 degrees N, by means of the RAPID/MOCHA mooring array between April 2004 and October 2007. The major density anomalies are found in the upper 500 m, and they are often coherent down to 1400 m. The densities have 13-day fluctuations that are apparent down to 3500 m. The two strategies for measuring eastern-boundary density - a tall offshore mooring (EB1) and an array of moorings on the continental slope (EBH) - show little correspondence in terms of amplitude, vertical structure, and frequency distribution of the resulting basin-wide integrated transport fluctuations, implying that there are significant transport contributions between EB1 and EBH. Contrary to the original planning, measurements from EB1 cannot serve as backup or replacement for EBH: density needs to be measured directly at the continental slope to compute the full-basin density gradient. Fluctuations in density at EBH generate transport variability of 2 Sv rms in the AMOC, while the overall AMOC variability is 4.8 Sv rms. There is a pronounced deep-reaching seasonal cycle in density at the eastern boundary, which is apparent between 100 m and 1400 m, with maximum positive anomalies in spring and maximum negative anomalies in autumn. These changes drive anomalous southward upper mid-ocean flow in spring, implying maximum reduction of the AMOC, and vice-versa in autumn. The amplitude of the seasonal cycle of the AMOC arising from the eastern-boundary densities is 5.2 Sv peak-to-peak, dominating the 6.7 Sv peak-to-peak seasonal cycle of the total AMOC. Our analysis suggests that the seasonal cycle in density may be forced by the strong near-coastal seasonal cycle in wind stress curl.