过去2000年全球典型暖期特征与机制的模拟研究

MODELING STUDY ON THE CHARACTERISTICS AND MECHANISMS OF GLOBAL TYPICAL WARM PERIODS OVER THE PAST 2000 YEARS

本文利用美国国家大气研究中心（NCAR）的通用地球系统模式（Community Earth System Model,简称CESM）的低分辨率版本（CESM1.0.3,T31_g37）在国际国内率先进行了多组过去2000年瞬变积分模拟试验,在与历史重建资料和观测资料进行对比验证的基础上,对过去2000年中的典型暖期（中世纪暖期与现代暖期）的特征和成因机制进行了初步探讨,结果表明：中世纪暖期太阳辐射加强是导致其“暖化”的主要原因之一,而温室气体浓度的激增是现代全球变暖的最主要原因;在中世纪暖期,自然因子（包括太阳辐射和火山活动）对降水量的影响之和比温室气体的影响高一个数量级;而在现代暖期,温室气体对降水量的影响比自然因子（包括太阳辐射和火山活动）对降水量的影响之和高一个数量级;在不同外强迫条件下的海表温度变化在热带太平洋区域截然不同,即自然因子影响下为类-拉尼娜态,而温室气体影响下为类-厄尔尼诺态;无论在中世纪暖期还是现代暖期,相对于1000～1850年的平均情况,沃克（Walker）环流均处于增强状态.

In this study,we employed the Community Earth System Model （CESM） from the National Center for Atmospheric Research （NCAR） with the low resolution （T31_ g37,which is equivalent to 3.75°×3.75°）,one free forcing simulation experiment （control run）,four single forcing experiments,including solar forcing run,volcanic forcing run,well-mixed greenhouse gas （GHGs） forcing run,and land use/Land cover （LUCC） forcing run,and one all four-forcing run were conducted for the past 2000 year.Because of lacking the reconstructed volcanic data,there is no volcanic forcing during 1～500A.D.in the all four-forcing run and volcanic forcing run.Based on the comparison of simulated results with proxy records and observed data,the CESM＇s performance of simulating global climate change was verified.Then the characteristics and mechanisms of the variability of the global surface air temperature and precipitation in the typical warm periods,i.e.,Medieval Warm Period （MWP,1101 ～ 1200A.D.） and Present Warm Period （PWP,1901～2000A.D.） during the past 2000 years was analyzed.All the conclusions are based on the modeling outputs.The results show：（1） The solar forcing is the main cause of MWP warming and the GHGs forcing is the dominant factor of PWP warming.The total solar irradiation is also contributed to the PWP warming.（2） The increment of precipitation that is induced by the natural forcings （solar activity plus volcanic eruption） is one order of magnitude higher than that induced by GHGs forcing in MWP,while in PWP,it is just the opposite,that is the GHGs forcing in PWP is one order of magnitude higher than that induced by natural forcings.（3） The responses of spatial patterns of the sea surface temperature to the natural （solar activity plus volcanic eruption） and anthropogenic （GHGs） forcings are different,especially over the tropic Pacific regions.It is the La Nina-like pattern in MWP and the El Ni（n）o-like pattern in PWP.（4） Relative to the average over the 1000～ 1850A.D.period,the Walker Circulation is intensified both in MWP and PWP.Overall,our experiments are using the most amplitudes reconstructed solar forcing,whether the other reconstructed solar irradiations or the other Earth/Climate System models could draw the same conclusions,it is definitely worth exploring.