青藏高原加热引起的海陆热力差异对新疆夏季降水的影响机理研究

The thermal action over the Tibetan Plateau (TP) plays an important role in the process of atmospheric circulation formation and maintenance in the Northern Hemisphere, and the regional thermal contrast caused by the summer heating over the TP has more important effect on weather and climate over its surrounding area. The previous studies in the effect of regional thermal contrast over the TP and its surrounding area on summer rainfall in China were more focused on the monsoon area, and less attention was paid to arid area in northwest China. The application is focused the mechanism problems, which the thermal contrast over the TP and its surrounding area affected summertime rainfall in Xinjiang, and studied the causes of large scale circulation adjusting, which can lead to the summer precipitation anomalies in Xinjiang by diagnostic analysis and numerical simulation. From the point of zonal thermal contrast between the TP and the Iran Plateau (IP), the relative contribution on the center moving of the South Asia High is differentiated from the seasonal variation of sensible heat and latent heat over the TP and IP, and we can deepen the understanding of the conversion process of the Tibetan High and the Iran High and the north-south oscillation of Iran Subtropical High affected by the zonal thermal contrast. From the point of meridional thermal contrast between the TP with IP and the Indian Ocean, the influencing processes of water vapor transporting northward from tropical Ocean are differentiated from the heating in the TP with the IP and their relative contribution for summer rainfall in Xinjiang, in addition, the impact way of water vapor transporting northward from tropical Ocean is revealed from the thermal contrast between the TP with the IP and the Indian Ocean. Above all can be contributed to explain the possible mechanism of dry-wet variation in Xinjiang.

青藏高原热力作用是形成和维持北半球大气环流的重要原因之一，夏季高原加热引起的区域热力差异对其周边地区天气气候有更大的影响。已有研究更多集中在东亚季风区，较少关注干旱区。本项目围绕青藏高原加热引起的海陆热力差异对新疆夏季降水的影响机理问题，利用诊断分析和数值模拟的方法研究大地形加热引起新疆夏季降水异常大尺度环流调整的原因。从青藏高原和伊朗高原纬向热力差异的角度，弄清青藏和伊朗高原感热和潜热加热季节变化对南亚高压中心位置移动的相对贡献，加深对纬向热力差异在伊朗副高南北振荡和南亚高压双模态转换过程中作用的理解。从青藏高原、伊朗高原和热带印度洋经向热力差异的角度，区分两个高原在水汽向北输送过程中的影响差异及对新疆夏季降水的相对贡献，揭示青藏高原和印度洋与伊朗高原和印度洋的经向热力差异在热带水汽向北接力（两步）输送过程中的影响途径。从大地形加热引起区域热力差异的角度解释新疆干湿变化的可能机理。

青藏高原热力作用是形成和维持北半球大气环流的重要原因之一，夏季高原加热引起的区域热力差异对其周边地区天气气候有更大的影响。本项目围绕青藏高原加热引起的海陆热力差异对新疆夏季降水的影响机理问题，利用诊断分析和数值模拟的方法研究大地形加热引起新疆夏季降水异常大尺度环流调整的原因。从纬向热力差异的角度，发现当5月青藏高原感热偏弱，伊朗高原感热偏强时，新疆北部夏季降水偏多；青藏高原加热减弱后，有利于南亚高压双体型频数的增多，利于塔里木盆地夏季降水增多。青藏高原加热主要影响对流层中高层环流变化，形成有力的动力条件，伊朗高原对印度洋水汽向北输送具有重要影响，形成有力的水汽输送条件；夏季感热加热是伊朗高原的主导加热形式，潜热加热是青藏高原的主导加热形式，伊朗高原和青藏高原中西部加热强度的变化，是导致伊朗高压型中心东西移动的主要因素，而伊朗高压中心南北移动则与帕米尔高原和阿拉伯半岛加热密切相关。从经向热力差异的角度，青藏高原和其西北干旱区存在明显热力差异，当高原加热减弱，其西北干旱区加热偏强时，新疆北部夏季降水发偏多；夏季青藏高原季风会导致高原西北部对流层中高层温度降低，同时印度洋变暖导致南亚对流层温度偏高，形成中亚-南亚热力差异，与塔里木盆地夏季降水联系紧密。南亚热力暖异常易于水汽输送第一步反气旋环流的形成，中亚热力冷异常易于水汽输送第二步气旋性环流的形成，导致热带海洋水汽两步输送至塔里木盆地，利于该区域夏季降水增多；青藏高原季风和南亚季风是青藏高原和热带印度洋热力加热的产物，当高原季风偏强，南亚季风偏弱时，对应中亚对流层中高层温度偏低，导致西亚急流位置偏南，中亚500 hPa为异常气旋控制，塔里木盆地盛行异常偏南风，同时印度半岛底层为反气旋环流，将热带水汽输送至中纬度地区，配合中亚气旋环流，进一步将水汽输送至塔里木盆地，形成有利于降水的环流和水汽条件。