4次大暴雨过程雷达径向速度和超低空西南急流特征分析

Analysis on radial velocity and ultra-low-level jet characteristics of four torrential rain processes

利用多普勒天气雷达VWP资料,结合探空资料和降水实况,对4次大暴雨降水过程雷达径向速度和超低空西南急流特征进行了分析。4次强降水过程有3次属于低槽冷锋类,1次属于切变线类,K值较大,850 h Pa与500 h Pa温差较小,较弱的垂直风切变,中低层具有充沛水汽。低层具有相似的流场结构,径向速度上零速度线表现为"S"型,即暖平流结构。上游超低空风速≥10 m·s-1,上下游雷达之间出现≥5 m·s-1的风速差之后,两部雷达之间出现小时雨量30 mm以上的强降水;上游超低空急流达到12 m·s-1以上,并且上下游超低空风速差超过15 m·s-1,降水强度进一步加强并维持。超低空急流的建立与维持,同时上下游雷达之间的超低空强辐合,为降水风暴的发展与维持提供了能量、水汽与动力条件,对强降水的形成与持续具有重要作用。

Using the Doppler weather radar data,combined with the sounding data and precipitation data,the mean radial velocity and ultra-low-level jet characteristics of four torrential rain processes were analyzed.The results show that four torrential rain processes had higher K value,smaller temperature difference between850 h Pa and 500 h Pa,abundant water vapor and weaker vertical wind shear in middle and lower layers.Similar flow field structure in low-level and ＂S＂type zero radial velocity contour of four torrential rain processes indicated that warm air advection was occurring.30 mm or more hourly rainfall occurred when the ultra-low-level wind speed（ from radar VWP products） reached 10 m·s-1or above and wind speed difference between upstream and downstream radar exceeded 5 m·s-1.The ultra-low-level wind speed reached 12 m·s-1or more and wind speed difference between upstream and downstream radar exceeded 15 m·s-1,the precipitation intensity furtherly strengthened and maintained. The establishment and maintenance of the ultralow-level jet,and the ultra-low-altitude convergence between the upstream and downstream radar provide the energy,water vapor and dynamic conditions for the development and maintenance of the precipitation storm,and play an important role in the formation and persistence of the heavy rainfall.