青藏高原热力强迫对中国东部降水和水汽输送的调制作用

从4个方面综述了有关青藏高原大地形热力“驱动”对中国东部雨带和水汽输送特征及其年代际变化的影响作用的研究进展:(1)中国三阶梯大地形热力过程变化与季风雨带季节演进;(2) 青藏高原地-气过程热力“驱动”及其季风水汽输送结构;(3) 青藏高原积雪冷源对中国东部水汽输送结构及其雨带分布的影响;(4) 青藏高原视热源变化与雨带年代际变化相关特征及其可能调制。其主要研究结论是:(1)中国西部高原特殊三阶梯大地形结构强化了海-陆热力差异,尤其是高原大地形使地-气热力差异季节变化有由青藏高原向东北方向大地形区域延伸变化趋势,且其与季风雨带由东南沿海移向西北朝青藏高原与黄土高原边缘同步演进,两者似乎存在类似季节内演进的一种“动态的吸引”。(2)中国东部雨带时空变化特征和季风强弱变化趋势均与青藏高原热源强弱异常变化相对应。青藏高原热源异常影响低纬度海洋向陆地的水汽传输路径和强度,进而调制中国东部降水时空演变。在青藏高原热源强和弱年,中国降水变率空间分布特征分别为“北涝南旱”和“南涝北旱”。青藏高原视热源强(弱)异常变化“强信号”将对东亚与南亚区域的季风水汽输送结构,以及夏季风降水时空分布的变异具有“前兆性”的指示意义。(3)长江中下游地区作为独特南北两支水汽流的汇合带,该地区夏季青藏高原热源与水汽通量相关矢特征呈类似于青藏高原多雪与少雪年水汽通量偏差场中水汽汇合区显著特征差异,揭示了冬季青藏高原积雪冷源影响中国东部夏季长江流域梅雨水汽输送结构特征。(4)中国降水的年代际变化基本型态为中国东部呈“南涝北旱趋势”,西北区域呈现出“西部转湿趋势”。但基于近10年青藏高原春季视热源出现“降后回升”趋势,中国东部“南涝北旱”的降水格局已出现转折趋势。

A study of the role of the Tibetan Plateau's thermal forcing in modulating rainband and moisture transport in eastern China

This paper reviews the recent progress in the studies of effects of the Tibetan Plateau's thermal forcing on the rainband and moisture transport pattern and their decadal variability in eastern China in the four respects: (1) variations in the thermodynamic process of the three-ladder terrain in China and seasonal advance of the monsoonal rainband, (2) thermal forcing of the TP's land-air process and monsoonal vapour transport pattern, (3) cooling effect of the TP's snowcover on the distribution of moisture transport and rainband in eastern China, and (4) the relations of changes in the TP's apparent heat source and decadal variation in monsoonal rainband as well as the possible modulation.The major research results are concluded as: (1) The special three-ladder terrain in western China intensifies the thermal contrast between the land and the ocean. In particular, the cascade of western China's elevated lands with the seasonal variations in thermal forcing extending toward the northeast seems to act as a "dynamic attractor" driving the monsoonal rainband to move to the northwest.(2) The decreases/increases in the TP's heat source could lead to the anomalies in the pathway and strength of vapour transport from the low-latitude oceans to the continents, regulating changes in East Asian monsoons and the spatial-temporal evolvement of rainfall in China.During the TP's strong and weak heating years, the monsoonal precipitation patterns in China tend to be characterized as "North floods-South droughts" and "North droughts-South floods", respectively. As a strong precursor signal, the anomalies of heating over the TP result in distinctive patterns of moisture transport in the East and South Asian regions and summer precipitation in China.(3) The mid-lower reaches of the Yangtze River are a distinctive confluent area of southward and northward air flows, where the differences in summertime column vapour fluxes between winter high and low snow cover years of the TP-key area were in a similar pattern of correlation vector between the TP's summer heat source and vapour transport fluxes. The winter TP snow cover condition might significantly affect the structure of subsequent summer moisture transport for the Meiyu rainfall in the reaches of the Yangtze River. (4) The patterns of the inter-decadal variability in China's precipitation are generally identified with the pattern of "southern flooding and northern drought" as well as trends of turning wet in the west over the last decades. In association with the trends in the TP's spring apparent heat source rising again after a fall in recent 10 years, a turning point could be expected in the eastern China's precipitation patterns.