Modeling the Freshening and Cooling Event in the Subpolar North Atlantic Ocean and its Impact on Thermohaline Circulation

在过去的40年里，北大西洋副极地发生了大规模的、全深度的冷却和清新。与此同时，北欧海通过法罗岸海峡的溢流减少，这是《北大西洋公约》形成的一个关键过程。观测表明，北欧海和大西洋之间的相互作用可能在这一事件的发展中发挥了关键作用。PI建议使用数值模型来研究引起所观察到的变化的机制和相互作用，并评估它们对热带和亚热带大西洋的温盐环流和海洋环流的影响。由于这种交换所固有的动力学和尺度与公海上空的大气环流非常不同，大多数海洋大气环流模式（OGCM）还不足以模拟北欧海洋和大西洋之间的相互作用。在以前的NSF资助的支持下，PI和Jim Price博士开发了一个耦合OGCM/边缘海模型，其具体目的是将其应用于北大西洋副极地。这个耦合模型代表了一个国家的最先进的数值工具，用于研究北欧海溢出，密度流夹带在陆架断裂，和开放的海洋过程之间的相互作用。该模式将用于解决（1）北大西洋涛动在过去40年中的持续正态是如何形成的？（2）通过丹麦海峡和法罗岸海峡的溢流对北欧海淡水强迫的响应;（3）溢流源水的淡化作用对北欧海淡水强迫的影响。结果表明：（1）NH_4 ~+-NH_3 ~+-NH_4 ~+-NH_3 ~+-NH_4 ~+

ABSTRACTOCE-0351055Large-scale and full-depth cooling and freshening have occurred in the subpolar North Atlantic Ocean in the last four decades. This was accompanied by a reduction of the Nordic Seas overflow through the Faroe Bank Channel, a key process for the NADW formation. Observations indicated that interaction between the Nordic Seas and the Atlantic Ocean may have played a key role in the development of this event. The PI proposes to use numerical models to study mechanisms and interactions that give rise to the observed changes, and to assess their impacts on the thermohaline circulation (THC) and on ocean circulations in the tropical and subtropical Atlantic Ocean. Since the dynamics and scales inherent to such exchanges are very different from that of the general circulation over the open ocean, most ocean general circulation models (OGCMs) are not yet adequate for modeling interactions between the Nordic Seas and the Atlantic Ocean. Supported by a previous NSF grant, the PI and Dr. Jim Price have developed a coupled OGCM/marginal-sea model with the specific purpose of applying it in the subpolar North Atlantic Ocean. This coupled model represents a state of the art numerical tool for studying interactions among the Nordic Seas overflow, the density current entrainment at shelf breaks, and open ocean processes. The model will be used to address (1) how the sustained positive state of North Atlantic Oscillation in the last 4 decades a?ected the fresh water budget in the Nordic Seas; (2) how the overflow through the Denmark Strait and Faroe Bank Channel responded to the fresh water forcing in the Nordic Seas; (3) how the freshening of the overflowed source water a?ected the entrainment rate at shelf breaks and thus the property and production of NADW; (4) how the THC responded to changes in NADW production; (5) what role the wind-driven circulation played in this cooling and freshening event; (6) how the circulation in the low-latitude ocean responded to the NADW and THC changes.