低空急流在一次初春混合强对流天气过程中的作用

The Role of Low-level Jet in a Mixed Strong Convective Weather Process in Early Spring

利用常规气象观测资料、区域自动站资料、强天气监测资料以及NCEP 1°×1°逐6 h再分析资料,从影响系统、环境场条件以及低空急流对混合强对流天气的水汽、热力、动力影响的诊断分析入手,对2019年3月4—5日贵州大范围雷雨大风、冰雹、短时强降水和暴雨等混合强对流天气过程进行综合分析。结果表明:低空急流建立并呈爆发式增强,使中低层水汽输送和辐合加强,大气上干冷、下暖湿的特征更显著,中低空能量锋区加强,垂直风切变增大,动力辐合加强,同时"低层辐合、高层辐散"的抽吸结构长时间维持,为混合强对流天气的发生发展提供了重要条件。超前的500 hPa温度槽叠加在中低空强暖湿气流之上,触发锋前暖区强对流天气,强对流天气发生在低空急流发展增强至最强盛期间,主要分布在700 hPa和850 hPa温度脊区附近强暖湿不稳定区;4日夜间南支槽配合低空切变线和活跃的静止锋,共同触发锋后冷区强降水天气,强降水主要发生在低空急流和水汽辐合达到最强之后,强降水主要分布在低空急流左前侧、850 hPa切变线南侧及850 hPa和700 hPa饱和湿区重叠区内。

Mixed strong convective weather processes,including the large-scale thunderstorm,gale,hail,short-term heavy rainfall and rainstorm in Guizhou on March 4-5,2019,were analyzed based on the conventional meteorological observation data,regional automatic station data,strong weather monitoring data and NCEP 1°×1°reanalysis data every 6 hours.The analysis was conducted on the impact of the impact system,environmental field conditions and low-level jet toward water vapor,heat and dynamic effects.The results show that the low-level jet is established explosively to enhance the vapor transport and convergence in the middle and lower layers.It is distinctive that the upper atmosphere layer is dry and cold,and the lower layer is warm and wet.The energy in the middle and lower levels front area is strengthened;the vertical wind shear is increased;the dynamic convergence is strengthened,and the suction structure of the"low-level convergence and high-level divergence"is maintained long,providing a necessity for the occurrence and development of the mixed strong convective weather.The leading 500 hPa temperature trough superimposing on the middle and low level warm strong moisture flow triggers the strong convective weather in the warm area before the front of the front of the front.The strong convective weather occurs during the period from the development of the low-level jet to the strongest,mainly distributed in the warm strong and wet unstable area near the 700 hPa and 850 hPa temperature ridges.On the night of 4 th,the South Branch trough,together with the low-level shear line and the active static front,triggered the strong precipitation in the cold area after the front.The strong precipitation mainly occurs in the after the strongest convergence of low-level jet and water vapor and the beginning of weakening.The heavy rainfall area are mainly distributed in the front left side of low-level jet,the south side of 850 hPa shear line and the overlapping area of 850 hPa and 700 hPa saturated wet area.