陕北榆林两次夏季暴雨过程的对比分析研究

Analysis of Two Rainstorm Processes in Yulin Area of Shaanxi Province in Summer

利用自动气象站常规观测资料、MICAPES、NCEP FNL 1°×1°再分析资料,FY-2G红外云图,FY-2G TBB资料、CB多普勒雷达VCP21模式资料对陕北榆林2019年7月28-29日、2019年8月2-4日两次暴雨过程进行对比分析研究。结果表明:(1)前者副高西伸北抬,与西风槽带来的冷空气在陕北北部交绥,配合近地层切变线、辐合线的触发,促成了对流性暴雨的生成。后者为西风槽配合中低空强的气旋性辐合系统,低层东路冷空气及台风外围水汽的输送,为系统性暴雨形成的有利条件。(2)中层干空气侵入和低层冷垫都有利于降水加强,暴雨易出现于θse陡峭和密集区;高值位涡柱下侵位置对两种类型暴雨有指示意义,700 hPa湿正压与湿斜压的正负值过渡区对应暴雨的落区。(3)MβCS与涡旋云系中心对应暴雨强降水区。(4)当CR回波强度达50 dBz,VIL达30 kg·m-2,对应区域会出现短时强降水。当负速度面积大于正速度面积,零速度线呈S状,回波强度35~45 dBz,叠加逆风区有利于大面积强降水形成;当零速度线呈折角,表示有冷锋经过,配合45 dBz左右回波强度,冷锋经过地区降水加强,有利于形成系统性暴雨。

Based on the regular observation data of automatic weather station,MICAPES,1°×1°NCEP FNL analysis data,FY-2 G Infrared cloud,FY-2 G TBB data,CB Doppler radar VCP21 data to analyze two rainstorm processes in YuLin(July 28-29,2019 and August 2-4,2019).The results show that:(1)When the the subtropical high northwards and westwards,and the cold air brought by the westerly trough intersects in northern of Shaanxi,with the triggering of the near-layer shear line and convergence line,are favorable conditions for convective heavy rain;The westerly trough with low-altitude intensity cyclone convergence system,and the lower cold air from the east area and transportation of the water vapor around the typhoon are favorable conditions of systemic rainstorms;(2)The MβCS,and the center of the vortex cloud system corresponds to heavy rain area;(3)Intrusion of dry air in the middle layer and cold pads in the lower layer are conducive to the strengthening of precipitation.Rainstorms are prone to occur in steep and dense areas;the area is where high value vortex column starts to invade is conducive to the formation of convective heavy rain and systematic rainstorm;the transition zone between the positive and negative values of 700 hPa wet positive pressure and wet baroclinic pressure corresponds to the rainfall area;(4)The value of CR and VIL are better indication for Yulin convection Heavy rain.When the CR echo intensity reaches 50 dBz and the VIL reaches 30,there will be short-term heavy precipitation in the corresponding area.When the negative velocity area is greater than the positive velocity area,the zero velocity line is S-shaped,the echo intensity is 35-45 dBz.and the superimposed upwind zone is conducive to the formation of large areas of heavy precipitation;when the zero velocity line is at an angle,it indicates that a cold front is passing,with 45 dBz of the echoes around,the cold front is strengthened by precipitation in the area,which is conducive to the formation of systemic rainstorms.