不同间冰期东亚夏季风北界的位置变化及机制研究

Changes in the north boundary of the East Asian summer monsoon in interglacials of last 800 ka

本文采用海洋-大气耦合气候模式COSMOS(ECHAM5/JSBACH/MPIOM)探讨800 ka以来东亚季风区在不同间冰期的气候特征。本研究采取了Barker等2019年提出的有关间冰期暖期稳定态的定义,即全球冰量处于或接近最低值,且没有千年气候事件/冰融水事件发生的间冰期早期阶段,保证了试验设计的真实性。结果表明:11个间冰期相比于工业革命前(Pre-industrial,简称PI)时期,MIS1、MIS5.5、MIS7.3、MIS7.5、MIS9.3、MIS11.3、MIS13.1、MIS15.1和MIS17时期在中国中高纬度大部分区域地表温度升高,而MIS15.5和MIS19.3与之相反;除了MIS15.5时期在中国北方降水减少以外,其余间冰期在中国北方降水均增多。在MIS15.5时期,CO2浓度低于PI时期,近日点的经度与PI时期接近,但偏心率约是PI时期的3倍,使得该时期北半球夏季接收到更少的太阳辐射,海陆热力差异减弱,导致东亚夏季风减弱,季风北界南移;MIS19.3时期,由于轨道参数变化不大,使得海陆热力差异与PI相比变化不大,所以季风强度变化不大,季风北界位置基本不变。其中,北半球夏季太阳辐射高于PI时期的其他间冰期阶段,其季风北界向西北方向移动,与西太平洋副热带高压(西太副高)的强度和位置的相应变化有关。这表明夏季太阳辐射的变化可能通过西太副高调节中国北方降水,从而改变了东亚夏季风北界的位置。

In this work,we employed a fully coupled climate model,COSMOS(ECHAM5/JSBACH/MPIOM),to investigate climate responses in East Asian Summer Monsoon(EASM)regions to warm interglacial periods in the 800 ka.In contrast to previous studies in which peak warm interglacials are defined by highest boreal summer insolation,here we define that an equilibrated warm interglacial is a period with low global ice volume and no existences of millennial-scale climate variability after the preceding deglaciation.Therefore,the defined interglacials are real time intervals,which can be compared with paleoclimate reconstructions directly.Our results show that,compared with the Pre-industrial(PI)period,surface air temperature in most areas of middle-high latitude regions in China is increased,including MIS1,MIS5.5,MIS7.3,MIS7.5,MIS9.3,MIS11.3,MIS13.1,MIS15.1,and MIS17,while cooling is found in the MIS15.5 and MIS19.3.MIS15.5 is characterized by a decrease in precipitation in the Northern China,while an increase is found in the other interglacial periods.In MIS15.5,as a consequence of lower-than-PI summer solar radiation due to eccentricity-modulated precession as well as a low atmospheric CO2 level,the land-sea thermal contrast is weakened,which gives rise to a southward shift of the northern boundary of the EASM.In MIS19.3,similar orbital settings results in slight changes in the land-sea thermal contrast and hence the intensity of the EASM was almost unchanged.In the rest of interglacial periods with higher-than-PI boreal summer insolation,the EASM north boundary migrated northwest,in association with changes in intensity and position of the western Pacific Subtropical High(WPSH).This indicates that changes in boreal summer insolation might via the WPSH modulate northern China precipitation and hence the EASM north boundary.