东亚地区YoungerDryas气候突变的数值模拟研究

SIMULATION OF ABRUPT CLIMATE CHANGE IN EASTERN ASIA DURING YOUNGER DRYAS

Younger Dryas (YD)气候突变事件是近两万年中一次全球性的气候急剧变冷事件。文章试图在东亚地区YD事件的若干证据基础上,从海洋、冰盖和大气的热力学以及动力学角度出发,利用气候模拟方法就东亚地区YD气候突变的机制和一些成因假说进行敏感性试验。模拟结果表明,因淡水通量异常引起的海洋表面温度降低是YD形成的直接原因。海洋大气耦合作用对于YD传播强度及时间不同步具有重要作用。除北大西洋淡水通量异常的作用外,南半球海洋的淡水通量异常可能对东亚地区的YD事件有着更重要的贡献。海洋耦合大气环流模式模拟表明,东亚与欧洲降温具有不同步性,最大变化速率欧洲达到-0.122℃/a,东亚地区为-0.067℃/a。模拟结果与东亚地区YD时期的气候记录在特征上能够进行对比,反映了模拟试验的边界和强迫条件的设计接近东亚古气候状况,因而模拟结果对分析海洋、冰盖和大气的热力学以及动力学探讨揭示YD气候事件的物理机制和动力原因具有可靠的依据。

The abrupt climatic change event- Younger Dryas (YD) marks a rapid decreasing in global temperature, with average temperature dropping. The purpose of this study is to explore the possible causes and mechanisms of YD in eastern Asia by using global climate models. With our modeling approaches some sensitive simulations are carried out for verifying some hypothesis of the proposed causes of YD and to find potential physical and dynamical factors that contributed to the YD climate change in eastern Asia. The modeling results indicated that the melt fresh water from ice sheet is the direct extra forcing factor for YD climate change. The interaction and coupling between ocean and atmosphere and its intensity are important for the strength of propagating and time lag of YD from European to eastern Asia. Besides the melt fresh water from the northern Atlantic, the melt fresh water from Antarctic in the Southern Hemisphere may have played the same important role for the YD climate in eastern Asia. From coupled climate model ECHO-G, under the condition with inner oscillation of ocean-atmosphere, decreasing in temperature in eastern Asia is about two years lagging comparing with that in Europe. The maximum variability of temperature are -0.122℃/a in Europe and -0.067℃/a in eastern Asia, respectively. The climatic features from our modeling results are comparable to that from climatological records during the YD in eastern Asia. It suggests that the experimental design and the forcing fields in the simulation are close to the paleoclimate condition of YD in eastern Asia. Therefore, our simulated study is useful in understanding and exploring the physical and dynamical causes of YD and the interaction among ocean, ice sheet and atmosphere under such an extreme climatic condition.