一次南岭地区早春暴雨成因分析

Cause Analysis of Early Spring Heavy Rainfall in Nanling

利用常规观测资料、NCEP/NCAR再分析资料等,对2019年3月4—5日发生在南岭山脉附近的强降水天气进行综合分析。结果表明:短波槽活跃,低层急流强盛,特别是边界层急流、切变较长时间维持,为这次暴雨过程提供了很好的动力和水汽条件;水汽集中在800 hPa以下,主要是低层和边界层的水汽辐合;偏北气流南下过程中,与南方暖湿气流在南岭山脉地形影响下易形成边界层及地面的中尺度气旋,大尺度切变线、辐合线受山脉阻挡南推缓慢,增加强降水维持时间,气流持续汇集产生辐合,使得水汽通量辐合区位置与南岭山脉的位置、走向一致,降水增幅明显;早春时节的暴雨,一般热力条件差,着重关注水汽及动力条件,特别是出现低空急流和边界层偏南急流时,在有利的地形下易触发中小尺度扰动而出现强降水。

Using the conventional and NCEP/NCAR reanalysis data,the Causes of Early Spring heavy rainfall in 4-5 March 2019 in Nanling are analyzed.The results show that the heavy rainfall is mainly affected by active shortwave troughs,strong low-level jet,long-lasting boundary layer jet and strong convergence in the boundary layers.those plays the important role in dynamical and vapor transport condition of the formation of heavy rainstorm.The water vapor condition analysis showed that the vapors concentrate under the 800 hPa layer.It is mainly the moisture flux divergence in the lower-layer and boundary layer at lower-level.Under the influence of the topography in Nanling,the combination of the northward air flow and the warm flow in the south forms organized vortex structure formed on the boundary layer and the ground.The synoptic-scale shear line and convergence line are slowly pushed south by the barrier of Nanling.It increasing the time of heavy rainfall.The location of water vapor flux convergence area is consistent with the location and direction of Nanling because of continuous convergence of airflow.It makes precipitation increase significantly.Normally,Early Spring heavy rainfall has poor heat quantity.It should pay more attention to the water vapor and dynamic conditions,especially the low-level jet and the southern jet at the boundary layer.It is easy to trigger small and medium scale disturbance and strong precipitation under favorable terrain.