新疆南疆极端干旱区典型暴雨的水汽特征及触发机制分析

Analysis of the Water Vapor Characteristics and Trigger Mechanism for a Typical Heavy Rainstorm in the Extreme Arid Region of the Southern Xinjiang

为加强对南疆暴雨过程的水汽特征和触发机理的认识,利用FNL和ERA5再分析资料、地面自动气象站观测资料、 FY-2G静止卫星的黑体亮温(TBB)资料,对2019年6月24-28日南疆极端干旱区暴雨过程进行了分析。结果表明,此次南疆地区持续性强降水天气发生在"两槽两脊"的纬向环流形势下,巴湖低涡、伊朗高压脊和辐合线是导致此次强降水过程的主要天气系统。暴雨的水汽主要来自于大西洋、黑海、里/咸海、阿拉伯海和孟加拉湾沿着西北路径、偏西路径和西南路径到达南疆盆地。低空急流引导着偏西北和偏西路径的水汽输送到南疆盆地,西南路径的水汽则在南疆西部500 hPa气旋性风场、 200 hPa高空西南急流的引导下翻越青藏高原输送到南疆地区。水汽收支计算表明:水汽的输入主要集中在南边界对流层高层和北边界对流层低层和高层;水汽的输出集中在东边界对流层低层和高层。南疆盆地南侧高大陡峭地形(昆仑山脉)的阻挡,使得从北部侵入的主导气流在山前辐合生成的中尺度辐合线,是此次强降水的主要触发系统。辐合线以北的偏西北气流带来的水汽在山前堆积,在地形抬升作用下不断辐合并抬升,不稳定能量释放,对流系统在山前不断生成发展,造成和田等地区持续的强降水天气。

In order to strengthen our understanding of the water vapor characteristics and trigger mechanism of the rainstorm in southern Xinjiang, this paper analyzes a rainstorm process occurred over southern Xinjiang region during 24-28 June 2019. Various data includingFNL(NCEP final operational global analysis) and ERA5(fifth version of the European Centre for medium-range weather forecasts reanalysis model) reanalysis data, hourly observation data at the automatic meteorological station, the satellite equivalent blackbody brightness temperature data of FY-2G are used. The results show that the precipitation occurred under the background of synoptic circulation with “two-ridge and two-trough” pattern over the middle and high latitude, the low vortex of Balkhash Lake, the ridge of Iran and convergence line are the main weather systems leading to the heavy rainfall. The water vapor of the heavy rainfall mainly comes from the Atlantic Ocean, Black Sea, Rio/Aral Sea, Arabian Sea and Gulf of Bengal, along the northwest, partial west and southwest paths to the southern Xinjiang Basin. Water vapor from the northwest and west paths to the southern Xinjiang Basin are guided by the low-level jet, and from the southwest path is transported over the Qinghai-Xizang Plateau to the southern Xinjiang under the guidance of the 500 hPa cyclone wind field and the southwest high-level jet on 200 hPa in the western southern Xinjiang. Water vapor revenue and expenditure calculation shows that water vapor input is mainly concentrated on the high level of troposphere at the south boundary, low and high levels of troposphere at the north boundary;the output of water vapor is concentrated in the low and high layers of the troposphere at the east boundary.The convergence line is the most important trigger system for this heavy rainfall, whose form is caused by the convergence of the dominant air flow invaded from the north in front of the high and steep terrain(KunLun Mountains) on the south side of the southern Xinjiang Basin. Meanwhile, the accumulation of water vapor brought by the northwesterly airflow in the north of the convergence line in front of the mountain is sufficient which is favorable for the rainstorm. Under the impact of terrain uplift, accompanied with the uplifting of air mass and accumulation of water vapor at the foothill of KunLun mountains, unstable energy is released and the convection system constantly generates and develops near the mountains, bringing continuous heavy rainfall to Hotan region.