变暖背景下青藏高原夏季风变异及其对中国西南气候的影响

利用1951—2012年逐月NECP/NCAR-Ⅰ再分析资料和1960—2012年逐月中国西南地区116站常规气象要素资料,基于青藏高原地区夏季600 hPa涡度场特征,定义了新的青藏高原夏季风强度和位置指数,讨论在全球变暖背景下,青藏高原季风变化对中国西南地区气候的影响。青藏高原季风强度整体增强,在20世纪90年代末达到峰值后逐渐减弱,与北半球气温变化具有较好的一致性,位置变化相对独立。夏季青藏高原季风强度和中心经度位置对中国西南地区气候有显著影响。当青藏高原季风偏强时,西南地区水汽异常辐合,以阴天为主,日照偏短,蒸发减弱,气温日较差明显减小,降水偏多;上升运动在川渝地区发展深厚,云贵地区仅限于600 hPa以下,川渝地区气象要素变化更显著。当青藏高原季风位置偏东时,西南全区受异常下沉运动控制,气温偏高,四川中、西部和贵州、广西等地出现较强的水汽异常辐散,气温显著偏高,相对湿度偏低,降水偏少。进入21世纪以来,青藏高原季风强度和中心经度的反位相叠加,加剧了西南地区的干旱化。新的青藏高原季风指数不仅能反映青藏高原地区的季风环流特征,而且对中国西南气候变化具有较好的指示意义,可为中国汛期气候预测提供理论依据和技术支持。

Variation of the Tibetan Plateau summer monsoon under the background of global warming and its impact on the climate in southwestern China

The new Tibetan Plateau (TP) summer monsoon indices were defined according to the vorticity characteristics at 600 hPa over the TP, and their impacts on the southwestern China climate had been analyzed by using the NCEP/NCAR reanalysis data from 1951 to 2012 and the surface meteorological data at 116 stations in southwestern China from 1960 to 2012 under the background of global warming. The intensification of the TP summer monsoon has reached the peak in the late 1990s, consistent with the global warming trend, but the locations are different from each other. There are two indices, the intensity and the position of the central longitude of the TP summer monsoon, which have significant effects on the southwestern China climate change. A stronger TP summer monsoon is favorable for more moisture convergence, more cloudy and rainy days, less sunshine, weaker evaporation and smaller diurnal temperature range in southwestern China. Moreover, the meteorological elements vary more significantly in the Sichuan-Chongqing region with the deep updraft development than in the Yunnan-Guizhou region with the ascending flow limited to below 600 hPa. When the central longitude moves to the east, the whole southwestern China is controlled by the abnormal sinking motion, which contributes to a higher temperature. There appears abnormal strong moisture divergence in the middle-western part of Sichuan, Guizhou, and Guangxi, which result in higher temperature, lower humidity and less rainfall over the above regions. Since the 21st century, the shrinking intensity and eastward-moving of the TP summer monsoon conspire to cause the drying trend of southwestern China. The new TP summer monsoon indices can not only reflect the monsoon circulation on the TP, but also have a good relationship with the climate change in southwestern China. This research provides a theoretical foundation for the drought-flood prediction of southwestern China.