A possible mechanism for the strong weakening of the North Atlantic subpolar gyre in the mid‐1990s
A possible mechanism for the strong weakening of the North Atlantic subpolar gyre in the mid‐1990s
复制标题
20世纪90年代中期北大西洋副极地环流强烈减弱的可能机制
DOI：
10.1029/2009gl039166
复制
发表时间：
2009
影响因子：
5.2
通讯作者：
M. Bentsen
中科院分区：
文献类型：
--
作者：
K. Lohmann;H. Drange;M. Bentsen
北大西洋副极地环流（SPG）的范围和强度在 20 世纪 90 年代中期迅速变化，从 1995 年的大而强到随后几年的大幅减弱。 SPG强度的突然变化通常与1995/96冬季北大西洋涛动（NAO）指数的逆转有关，从强正值变为负值。在本研究中，我们通过 NCEP-NCAR 再分析场驱动的海洋环流模型研究了 SPG 的初始状态对其后续行为的影响。我们的敏感性积分表明，SPG 的减弱不能仅用大气强迫的变化来解释。相反，在 1995 年左右的时间段内，无论实际的大气强迫如何，SPG 都即将减弱，因为海洋状态在之前七年（1989-1995）期间受到持续强的正 NAO 的控制。我们的分析表明，正是海洋的这种预处理，加上1995/96年NAO的突然下降，导致了1990年代后半期SPG的强烈而迅速的减弱。正如最近提出的那样，这一假说解释了 1995 年之后 SPG 强度和大气强迫（冬季 NAO）的不同演变。
The extent and strength of the North Atlantic subpolar gyre (SPG) changed rapidly in the mid‐1990s, going from large and strong in 1995 to substantially weakened in the following years. The abrupt change in the intensity of the SPG is commonly linked to the reversal of the North Atlantic Oscillation (NAO) index, changing from strong positive to negative values, in the winter 1995/96. In this study we investigate the impact of the initial SPG state on the subsequent behavior of the SPG by means of an ocean general circulation model driven by NCEP‐NCAR reanalysis fields. Our sensitivity integrations suggest that the weakening of the SPG cannot be explained by the change in the atmospheric forcing alone. Rather, for the time period around 1995, the SPG was about to weaken, irrespective of the actual atmospheric forcing, due to the ocean state governed by the persistently strong positive NAO during the preceding seven years (1989–1995). Our analysis indicates that it was this preconditioning of the ocean, in combination with the sudden drop in the NAO in 1995/96, that lead to the strong and rapid weakening of the SPG in the second half of the 1990s. This hypothesis explains the diverging evolution of the strength of the SPG and the atmospheric forcing (winter NAO) after 1995, as has been suggested recently.