丹麦海峡环流在北大西洋高纬度海区降温现象中的作用

The subpolar North Atlantic, connected with the Nordic Seas through Denmark Strait, is an important generating region for the Atlantic meridional overturning circulation (AMOC). Recent observational studies suggest that the subpolar cooling in the North Atlantic Ocean has repeatedly appeared in opposition to global surface temperature increasing. In many coupled climate models, AMOC oscillations are considered as one possible physical basis for this temperature changes, however, there is as yet no clear understanding of the immediate causes for the temperature decreasing in either the models or observations. An issue highly pertinent to the understanding of decadal climate predictability and to the discussion of the role of oceans in climate change is by what and how the subpolar cooling in the North Atlantic is excited. This proposal represents a systematic approach toward understanding this important issue with a high resolution regional ocean model. In particular, we seek to explore how the subpolar temperature is affected by the circulation in the Denmark Strait, and what is the subpolar temperature’s response to future global climate change. A set of carefully designed numerical experiments will be conducted and thoroughly analyzed to test the following scientific hypotheses: 1) the circulation change in Denmark Strait plays a key and direct role in the subpolar cooling of North Atlantic Ocean; 2) the changes in the Nordic Seas in response to global warming may contribute significantly to the subpolar cooling under global warming scenarios by the circulation change in the Denmark Strait. The proposed results will offer a brand new perspective to explain the repeatedly occurred subpolar cooling in the North Atlantic Ocean.

通过丹麦海峡与北欧海相连的北大西洋高纬度海区，是大西洋经向翻转流生成的重要区域。观测资料研究表明该海区曾多次出现与全球表层温度变化相左的降温现象，但目前对其降温机制还不是很清楚。因此作为理解年代际气候可预报性以及海洋在气候变化中的作用的重要议题之一，北大西洋高纬度海区降温的直接触发机制就成为一个亟待研究的命题。本项目拟利用一个区域高分辨率海洋模式深入研究在气候变暖背景下北大西洋高纬度海区降温现象的产生机制及其影响，特别关注丹麦海峡环流等重要物理过程在其中所起的作用以及对未来气候变化的响应问题。通过一系列数值试验和结果分析，预期可以验证：1）丹麦海峡的环流变化是引起该海域温度下降的直接原因；2）北欧海对气候变暖的响应可以有助于预测未来气候变暖情景下北大西洋高纬度海区的温度变化规律。本项目的预期研究成果将为解释该海区的温度异常现象提供一种全新的思路。

北大西洋高纬海区是大西洋经向翻转流、北大西洋深层水生成的重要区域，对气候研究及预测具有重要作用。课题利用高分辨率的区域模式成功再现了北大西洋高纬海区降温现象的基本特征，并分析了丹麦海峡环流变化等过程对此降温特征的影响及机制；提出了在中高纬海区的高频“天气噪声”可能是大西洋经向翻转环流维持其强度、变化的重要因素，而下层的北大西洋深层水可以在内区存在着与常规认知不同的特殊的输运通道。此外，课题拓展了大西洋赤道区域的相关科学问题。利用同化资料及简化模型，发现赤道西边界流经向输运季节变化的反对称性与纬向风所激发出来的对称的赤道罗斯贝波有关。另外基于全耦合模式，证明了大气跨赤道的能量输运主要与活跃的海洋动力过程有关。项目的研究结果能够提高我们对北大西洋海区海洋动力环境的认识，有助于我们深入了解区域性的海洋环境对未来气候变化的响应。课题组在相关学术刊物上已发表论文7篇，其中SCI论文5篇，已取得的研究成果对北大西洋翻转环流及深层水相关问题的研究具有重要的参考价值，为下一步继续探索该领域的其它科学问题打下了坚实的基础。