过去千年年代和百年尺度东亚夏季风变化的模拟分析

利用通用地球系统模式过去千年集成（CESM-LME）试验数据，在验证模式模拟能力的基础上，分析了过去千年（850~1849年）年代和百年尺度东亚夏季风变化及其与中国东部夏季降水的关系。总体上，东亚夏季风在过去千年逐渐减弱，并伴随着年代际和百年尺度波动。在变化趋势上，过去千年土地利用不断增加、后期火山爆发偏多和地球轨道参数变化联合引起欧亚大陆中高纬表面温度降低、东亚区域海陆热力差异减小，东亚夏季风相应减弱；在年代际尺度上，东亚夏季风变化与太平洋年代际振荡有关，后者通过影响北太平洋和中国东部表面温度来改变东亚区域海陆热力差异和夏季风强度；百年尺度东亚夏季风波动受多种因子共同调制，期间欧亚大陆中高纬和北太平洋表面温度变化明显。与此同时，过去千年东亚夏季风逐渐减弱伴随着中国东部降水由南向北呈现负—正—负的变化趋势；在年代际和百年尺度上，东亚夏季风偏强时，中国东部降水表现为南旱北涝型分布。

A modeling analysis of East Asian summer monsoon changes on interdecadal and centennial timescales during the last millennium

Using the outputs of the Community Earth System Model Last Millennium Ensemble(CESM-LME) experiment, we first evaluate the ability of the model in reproducing the climatology in association with the East Asian summer monsoon, and then investigate the East Asian summer monsoon changes on interdecadal and centennial timescales and their relationship with the eastern China summer precipitation during the last millennium(850~1849 A.D. in this study). It is found that the East Asian summer monsoon has a weakening trend during the last millennium and displays prominent interdecadal and centennial variations. The weakening trend is related to increased land use over time, more volcanic eruptions in the later period, and orbital parameter changes during the last millennium, which reduce the surface air temperature over the middle and high latitudes of Eurasia and in turn the land-ocean thermal contrast in East Asia, thus weakens the East Asian summer monsoon. Interdecadal variations are closely related to the internal variability of Pacific Decadal Oscillation, which modifies the land-ocean thermal contrast and monsoon in East Asia by promoting the surface air temperature changes over the North Pacific and eastern China. On the centennial scale, the monsoon variations are affected by various factors, which induce obvious changes of surface air temperature over both the middle and high latitudes of Eurasia and North Pacific and thus impact the East Asian summer monsoon. Meanwhile, the weakening trend of East Asian summer monsoon is accompanied by negative-positive-negative trend of precipitation change from South to North China during the last millennium; on decadal and centennial scales, the summer precipitation deficit and excess occur in southern and northern China, respectively, when the East Asian summer monsoon is strong.