The Mean State and Variability of the North Atlantic Circulation: A Perspective From Ocean Reanalyses
The Mean State and Variability of the North Atlantic Circulation: A Perspective From Ocean Reanalyses
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DOI：
10.1029/2019jc015210
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发表时间：
2019-12-17
影响因子：
3.6
通讯作者：
Zuo, H.
中科院分区：
文献类型：
--
作者：
Jackson, L. C.;Dubois, C.;Zuo, H.
过去几十年来，通过地下剖面浮标和卫星观测以及最近监测大西洋经向翻转环流（AMOC）的努力，北大西洋周围的观测网络得到了显着改善。这些显示了北大西洋十年来的时间尺度变化，包括热含量、热传输和环流。然而，观测覆盖范围仍然存在显着差距。海洋再分析将观测结果与动态一致的海洋模型相结合，可用于了解观测到的变化。然而，还必须评估重新分析代表动态的能力。我们使用全球海洋再分析集合来检查 1993 年以来北大西洋的时间平均状态和年际-十年间变化。我们评估再分析能够在多大程度上捕获过程以及是否可以获得任何理解。我们特别研究了环流的各个方面，包括对流、AMOC 和环流强度以及传输。我们发现，重新分析显示出一定的一致性，特别是显示从 1990 年代中期到至少 2009 年，副极地环流和北纬 50 度 AMOC 减弱（与之前研究中的年代际变化有关），自 2000 年以来北纬 26.5 度 AMOC 增强然后减弱，以及环流变化对运输的影响。这些结果与模型研究和自 2005 年以来在北纬 26.5 度的 AMOC 观测结果一致。我们还发现整个 AMOC 强度和混合层深度的分布较小，这表明随着观测覆盖范围的扩大而有所改善。
The observational network around the North Atlantic has improved significantly over the last few decades with subsurface profiling floats and satellite observations and the recent efforts to monitor the Atlantic Meridional Overturning Circulation (AMOC). These have shown decadal time scale changes across the North Atlantic including in heat content, heat transport, and the circulation. However, there are still significant gaps in the observational coverage. Ocean reanalyses integrate the observations with a dynamically consistent ocean model and can be used to understand the observed changes. However, the ability of the reanalyses to represent the dynamics must also be assessed. We use an ensemble of global ocean reanalyses to examine the time mean state and interannual-decadal variability of the North Atlantic ocean since 1993. We assess how well the reanalyses are able to capture processes and whether any understanding can be gained. In particular, we examine aspects of the circulation including convection, AMOC and gyre strengths, and transports. We find that reanalyses show some consistency, in particular showing a weakening of the subpolar gyre and AMOC at 50 degrees N from the mid-1990s until at least 2009 (related to decadal variability in previous studies), a strengthening and then weakening of the AMOC at 26.5 degrees N since 2000, and impacts of circulation changes on transports. These results agree with model studies and the AMOC observations at 26.5 degrees N since 2005. We also see less spread across the ensemble in AMOC strength and mixed layer depth, suggesting improvements as the observational coverage has improved.