全新世北半球中纬度降水变化对不同外强迫响应的模拟研究

Simulation of northern hemisphere mid-latitude precipitation response to different external forcings during the Holocene

北半球中纬度(30°~50°N)降水变化一直是当今社会关注的热点。文章基于重建资料、气候系统模式CCSM开展的TraCE-21 ka瞬变试验和地球系统模式CESM完成的NNU-12k瞬变加速气候模拟试验结果,探讨了全新世以来中纬度降水变化趋势及其对外强迫的响应。结果表明:全新世以来重建的中纬度降水呈增加趋势,在距今10~7 ka,TraCE-21 ka全强迫试验模拟出了这一趋势,主要受陆地冰盖衰退、淡水注入和轨道参数(ORB)的共同影响。在7~0 ka,NNU-12k的ORB试验与重建的降水增加趋势一致,但主要集中在海洋地区。两个模式均模拟出了欧亚大陆中纬度地区比北美大陆干燥的趋势特点,并发现是ORB的作用引起的;而温室气体(GHGs)主要对欧亚大陆降水增强有所贡献,但不能抵消ORB的负贡献。然而,模拟的中纬度降水对全新世以来ORB、GHGs的响应存在模式依赖性,这是今后重建-模拟资料对比时需要考虑的重要因素。

The Northern Hemisphere(NH)mid-latitude precipitation(30°~50°N)change is the focus of social attention.Using the reconstructions,the results of TraCE-21 ka experiments simulated by the Community Climate System Model 3(CCSM3),and the results of NNU-12k transient acceleration experiments simulated by Community Earth System Model(CESM),this study discuss the change of NH mid-latitude precipitation and its response to external forcing during the Holocene.The result shows that the reconstructed NH mid-latitude precipitation has increased since the Early Holocene.During 10~7 ka B.P.,a similar increasing trend occurs in the TraCE-21 ka all forcing experiment,which is mainly affected by the ice sheet recession,fresh water injection and orbit forcing(ORB).During 7~0 ka,the precipitation shows an increase trend in NNU-12k ORB experiment,which is consistent with the reconstructions,but the trend is concentrated in marine areas.Both models simulate a stronger drying trend over mid-latitude Eurasia than North America,which is induced by the ORB.Greenhouse gases(GHGs)mainly contribute to the enhanced precipitation in Eurasia,but it cannot offset the negative contribution of the ORB.However,during the Holocene,the response of simulated NH mid-latitude precipitation to ORB and GHGs is model dependent,which can be an important factor to be considered in the proxy-model data comparison.