LGM时期气候背景下中国区域植被变化对东亚夏季降水影响的模拟

利用CCM3/NCAR全球气候模式在21kaB.P.(2.1万年前)的末次盛冰期(LGM)气候背景下，对中国区域植被变化对夏季(6～7月)东亚季风降水的影响进行了模拟，结果表明： 在LGM时期气候背景下，植被退化会使得中国东南部夏季降水减少，其中东南沿海减少超过20mm，而在 100°E 以东的中国北方大部分地区降水增加，其中心值大于50mm，从而导致降水南少北多的现象，植被的这种影响可以从物理上得到解释。在LGM气候背景下，植被退化在暖季起着增温的作用，即通过影响地表热状况使夏季大陆增温，增强了夏季东亚大陆与其周边海域的热力差异，从而使夏季东亚地区的西南风增强，35°～45°N的北方地区对流层低层的空气辐合和对流层上升运动加强，伴随着在 30°N 以南的中国南方地区出现异常下沉运动； 同时，西南季风的加强也导致夏季在 30°～40°N 之间的华北地区低层水汽输送加大。在这些因子的共同作用下，中国北方夏季降水增多，而东南部降水减少。这些结果说明使用LGM时期中国区域不同的重建植被资料可以对东亚季风气候模拟产生一定的不确定性。因此，重建可信度高的东亚植被对于降低对气候模拟的不确定性是十分重要的。

MODELING OF IMPACTS OF REGIONAL VEGETATION CHANGE IN CHINA ON EAST ASINA SUMMER RAINFALL UNDER THE BACKGROUND OF THE LAST GLACIAL MAXIUM

In this study,by using the CCM3/NCAR global climate model,impacts of the vegetation change in China on the East Asian summer (June ～ July) monsoon rainfall were simulated under the background of the last glacial maximum (LGM) (about 21,000 calendar years ago). It was discovered that at the LGM, the vegetation degradation resulted in a decrease of the summer rainfall in South East China, with the central value of -20mm near the coasts of South East China, and an increase of the rainfall in most of North China east of 110°E, with its central value exceeding 50ram,which finally caused less (more)summer rainfall in South (North)China. This impact of the vegetation may be physically explained well. Under the background of the LGM climate,the vegetation degradation increased the local surface temperature through changing the surface thermal condition in a warm season, strengthening the thermal contrast between the East Asian land and its adjacent oceans and then the summer southwest monsoon over East Asia. Accordingly, both the low-level convergence of air mass and the tropospheric ascending motion strengthened over North China between 35°～ 45°N, while the anomalous descending motion appeared over South East China south of 30°N. Meanwhile,the strengthened southwest monsoon also increased the transport of water vapor toward to North China between 30°N and 40°N. These variations in the atmospheric circulations resulted in an increase of the summer rainfall in North China, accompanying with a decrease of the rainfall near South East China. This result implies that using the different LGM vegetation reconstructions in East Asia possibly produces some uncertainties in simulating the East Asian climate. Therefore, reconstructing more believable vegetation in East Asia is important to reduce the uncertainties.