地形对豫东南一次极端暴雪影响分析

为了更全面地认识豫东南极端暴雪发生发展的机制，利用常规探空和地面观测资料以及NCEP 1°×1°再分析资料，对2018年1月3-4日豫东南极端暴雪过程从环流背景，高低空急流配置及水汽输送等方面进行分析。结果表明：高空低槽、中低空急流及切变线同时配合地面强冷空气南下，是形成本次极端暴雪事件最根本的天气尺度条件；豫东南位于高低空急流耦合作用形成的强烈上升区，西南急流不但为暴雪区提供源源不断的水汽条件，还起到了动力抬升及不稳定能量释放等作用，有利于暴雪发生发展与维持。豫东南地处大别山脉与桐柏山脉东北侧迎风坡处，地形较复杂，为了探究地形对本次极端暴雪的影响，本文尝试通过WRF模式模拟豫东南地形对降水的影响，通过控制试验和敏感试验对比分析表明，山体的迎风坡一侧对降水的增幅作用达4-6 mm，而背风坡一侧对降水的减幅作用约为6 mm；低层的U风分析显示，地形消减后U风风速将减小2-4 m·s^-1，并且中心位置东南移1-2个纬距，强降水中心随之东南移；垂直速度沿经度及纬度剖面均显示山体迎风坡处对垂直上升运动增幅达0.1×10^-2 m·s^-1；地形对水汽辐合起到明显增强作用，尤其在山体上方850-700 hPa高度辐合更加显著。

Impact of terrain on an extreme snowstorm event in southeastern He'nan province

In order to fully understand the development mechanism of extreme snowstorm events in southeastern He'nan province,we analyzed the circulation background,the configuration of high-and low-level jets,and water vapor transport during an extreme snowstorm event in southeastern He'nan province from January 3 to 4,2018,using conventional sounding and ground observation data and National Centers for Environment Prediction (NCEP) 1°×1° reanalysis data.The results showed that the most fundamental synoptic-scale conditions for this event include low trough athigh levels,jets at low and middle levels,shear lines,as well as the southward motion of strong cold air.The southeastern part of He'nan province is located in a strong uplifting area due to the coupling effect of the high- and low-level jets.The southwesterly jets not only continuously provides plenty of water vapor to the snowstorm area,but also contributes to the dynamic lifting and unstable energy release,which favors the development and maintenance of the snowstorm event.The southeastern part of He'nan province is located on the northeastern side of the Dabie Mountains and Tongbai Mountains;the surrounding terrain topography is quite complicated.In order to explore the influence of topography on this extreme snowstorm event,we attempt to simulate the impact of southeastern terrain on precipitation using the Weather Research and Forecast (WRF) model. The comparison between control experiment and sensitivity experiment shows that the precipitation increases by 4-6 mm at the windward side and decreases approximate 6 mm at the leeward slope side.After terrain reduction,the U wind speed at low altitudes decreases by 2-4 m·s^-1,and it's center position moves towards the southeast by 1-2 latitudes,leading to the southeastward movements of strong precipitation center.The vertical velocity along the longitude and latitude profiles show that the vertical ascending motion at the mountain windward side increases by 0.1×10^-2 m·s^-1;topography significantly enhances the water vapor convergence,especially at 850-700 hPa above the mountains.