The Surface-Forced Overturning of the North Atlantic: Estimates from Modern Era Atmospheric Reanalysis Datasets
The Surface-Forced Overturning of the North Atlantic: Estimates from Modern Era Atmospheric Reanalysis Datasets
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DOI：
10.1175/jcli-d-13-00070.1
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发表时间：
2014-05-01
影响因子：
4.9
通讯作者：
Blaker, Adam T.
中科院分区：
文献类型：
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作者：
Grist, Jeremy P.;Josey, Simon A.;Blaker, Adam T.
给出了与北大西洋表面强迫倾覆有关的近期平均和时变水团变化率的估计。这些估计来自以下六个大气再分析：日本25年再分析(JRA)、NCEP-NCAR再分析(NCEP1)、NCEP-美国能源部(DOE)再分析(NCEP2)、欧洲中期天气预报中心(ECMWF)中期再分析(ERA-I)、气候预测系统再分析(CFSR)和现代研究和应用再分析(MERRA)，以及来自两个全球网格数据集(世界海洋地图集和气象局EN3数据集)的海面盐度场。由此得到的1979-2007年平均地表强迫流函数的12个估计值都描绘了一个亚极单体，最大值位于北纬45度以北，西格玛附近=27.5公斤m(-3)，以及一个位于北纬20度至40度之间，西格玛附近=26.1公斤m(-3)的副热带单体。亚极单体的平均震级变化在12-18Sv(1 Sv 10(6)m(3)S(-1))之间，这与地下观测对翻转环流的估计是一致的。对地表密度通量的热分量和盐度分量的分析表明，推断的低纬环流的巨大差异很大程度上是再分析净热通量场偏差的结果，全球平均热通量的范围为-13~19Wm(-2)。亚极细胞中时间变异性的不同估计彼此之间有很好的相关性。这表明，与选择再分析产品相关的不确定性并不会严重限制该方法推断亚极倾覆中的可变性的能力。相反，对副热带变率的不同估计彼此之间的相关性很差，并且它们中只有一个子集捕捉到了独立估计的北大西洋副热带模式水量的很大一部分变率。
Estimates of the recent mean and time varying water mass transformation rates associated with North Atlantic surface-forced overturning are presented. The estimates are derived from heat and freshwater surface fluxes and sea surface temperature fields from six atmospheric reanalysesthe Japanese 25-yr Reanalysis (JRA), the NCEP-NCAR reanalysis (NCEP1), the NCEP-U.S. Department of Energy (DOE) reanalysis (NCEP2), the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-I), the Climate Forecast System Reanalysis (CFSR), and the Modern-Era Reanalysis for Research and Applications (MERRA)together with sea surface salinity fields from two globally gridded datasets (World Ocean Atlas and Met Office EN3 datasets). The resulting 12 estimates of the 1979-2007 mean surface-forced streamfunction all depict a subpolar cell, with maxima north of 45 degrees N, near sigma = 27.5 kg m(-3), and a subtropical cell between 20 degrees and 40 degrees N, near sigma = 26.1 kg m(-3). The mean magnitude of the subpolar cell varies between 12 and 18 Sv (1 Sv 10(6) m(3) s(-1)), consistent with estimates of the overturning circulation from subsurface observations. Analysis of the thermal and haline components of the surface density fluxes indicates that large differences in the inferred low-latitude circulation are largely a result of the biases in reanalysis net heat flux fields, which range in the global mean from -13 to 19 W m(-2). The different estimates of temporal variability in the subpolar cell are well correlated with each other. This suggests that the uncertainty associated with the choice of reanalysis product does not critically limit the ability of the method to infer the variability in the subpolar overturning. In contrast, the different estimates of subtropical variability are poorly correlated with each other, and only a subset of them captures a significant fraction of the variability in independently estimated North Atlantic Subtropical Mode Water volume.