蒙古高原和云贵高原地形对亚洲气候的影响评估

Uplift of Tibetan Plateau is widely accepted to be one of the most important factors in modulating the evolution of global and Asian climate since Cenozoic. The plateau remarkably affects the stationary planetary wave over northern hemisphere and the monsoon-arid system over Asia by its thermal and dynamical effects. However, in previous studies, the potential role of small topography around Tibetan Plateau (Mongolia, Yunnan-Guizhou etc) on climate system is often neglected because the small mountains are usually not resolved in numerical models. Our preliminary work indicates that the existence of Mongolian Plateau can significantly intensify the planetary waves and the westerly jet and the contribution is even larger than that of Tibet, which highlights the climatic importance of small topography. Thus, we propose in this project to conduct a thorough evaluation on the mechanical effect of Mongolian and Yunnan-Guizhou Plateaus and their influences on the evolution of Asian climate by numerical experiments and meteorogical data. The relative contributions between small mountains and Tibetan Plateau will be also compared. Through the integration of theoretical studies and tectonic/paleoclimate records, the influence of small topography around Tibetan Plateau and the mechanism on the coupling of westerly and monsoon over Asia and the drying processes in the inland basins are to be appealed, in order to better understand the role of tectonic uplifts in the Cenozoic climate evolution.

青藏高原隆升被公认是影响晚新生代全球及亚洲气候演化的重要因素之一，高原通过动力热力效应作用于北半球行星波及亚洲季风干旱系统。但已有研究受限于分辨率对地形的辨识大多集中于高原主体，严重忽视了高原周边规模较小地形(如蒙古,云贵等)对亚洲局地乃至全球气候形成演化的可能贡献。前期工作表明蒙古地形由于其特殊地理位置引发显著动力效应极大加强北半球行星波及西风急流，贡献甚至大于青藏高原主体，揭示了目前理论研究中得到的高原主体气候影响可能被高估，高原影响与其实际地形分布关系密切。本项目拟利用高分辨率气候模式辅以现代气象资料对蒙古和云贵高原地形的动力效应及其对亚洲气候的影响进行评估，区分其与高原主体的相对贡献。并将理论研究同古气候记录结合，揭示青藏高原周边山地的隆升对亚洲季风-西风耦合变化及内陆干旱的影响，深入理解构造隆升在新生代气候演化中所扮演的角色。

青藏高原隆升对亚洲季风干旱气候具有重要贡献，但青藏高原周边地形对季风及干旱气候形成有何影响，它们同青藏主体相对贡献如何，目前还不甚清楚。本项目通过建立理想气候模拟试验，评估蒙古高原、云贵高原、天山帕米尔等边缘地形对亚洲季风干旱形成及时空分异的影响。研究表明，青藏高原主体抬升可导致印度夏季风的增强和亚洲内陆降水的减少，其中云贵高原和蒙古高原对中亚地区降水减少的贡献可以达到青藏高原整体的一半，单独云贵高原对印度夏季风的影响是显著减弱的。就季节性而言，云贵和蒙古高原对中亚冬季的降水有更明显的抑制作用。而帕米尔高原和天山对亚洲内陆干旱区的时空分异起主要作用，在帕米尔—天山出现前，东部干旱区的降水季节性与西部相同，均为冬春雨降水最多而夏季降水最少。帕米尔—天山出现后，西部干旱区降水季节性得到一定程度的加强，而东部干旱区夏季降水显著增加而冬春季减少，从而东部干旱区降水季节性从冬春雨主导型转变为夏雨主导型。这些研究表明，并不是每个子区域都与青藏主体的气候效应一致，边缘地形的动力阻碍作用较为重要，尤其是处于典型敏感区的边缘地形很可能对某些气候系统具有极重要的作用。