长江横切变线影响的黔东北2类暴雨特征分析

Characteristics of Two Types of Rainstorms in Northeastern GuizhouAffected by the Transverse Shear Line over the Yangtze River

【目的】为探索黔东北受长江横切变线影响的暴雨特征和强降水形成原因。【方法】利用实况观测资料,NCEP 1°×1°再分析资料,对近10 a黔东北受长江横切变线影响的暴雨过程进行分类分析。【结果】(1)副热带高压西侧北上的西南暖湿气流与我国东北低涡槽南下的变性干冷空气在长江中下游—贵州北部交汇,使得中低层南北气流之间的横切变线维持。但地面上影响系统不同,造成暴雨落区、强度存在差异。(2)第1类暴雨,地面受低压影响,在充足的水汽和强的热力不稳定层结条件下,中低层强动力抬升及边界层锋生作用,强降水在地面辐合线与低层切变线叠加区域发生发展,雨强≥50 mm·h-1,50 mm≤24 h降雨量<100 mm;第2类暴雨,地面受海上高压后部偏东气流影响,在充足的水汽、强的动力抬升和弱的热力不稳定层结条件下,强降水在低层切变线附近及地面偏东气流里发展,暴雨范围较广,20 mm·h-1≤雨强<50 mm·h-1,局地24 h降雨量≥100 mm。【结论】通过分析黔东北受长江中下游切变线影响的2类暴雨特征及影响系统的异同,揭示暴雨差异及形成原因,以期提升此类暴雨预报能力。

To explore the characteristics of rainstorms and the formation causes of severe precipitation in the northeast part of Guizhou Province under the impact of the transverse shear line in the Yangtze River,this article analyzes the rainstorm processes in northeastern Guizhou affected by the Yangtze River transverse shear line in the past 10 years by using the observations and NCEP 1°×1°reanalysis data.The results show that:(1)The warm-humid southwestern air flowing northward from the west side of subtropical high pressure and the dry and cold air of the Northeast China low vortex trough flowing southward converge in the middle and lower reaches of the Yangtze River and the northern part of Guizhou,making the transverse shear line between the north and south airflows in the lower and middle layers maintained.However,different systems of shadow lines on the surface cause the differences in the area and intensity of rainstorms.(2)The first type of rainstorms is influenced by the surface low pressure.Under sufficient moisture and strong thermodynamically unstable stratification conditions,strong dynamic uplift in the middle and lower layers and boundary layer frontogenesis,severe precipitation occurs and develops in the superposition area of the surface convergence line and the low-level shear line,with the hourly rainfall intensity exceeding 50 mm and the 24 h rainfall more than 50 mm and less than 100 mm.The second type of storm is impacted by the easterly airflow behind the offshore high pressure.Under the conditions of sufficient moisture,strong dynamic uplift and weak thermodynamically unstable stratification,severe precipitation develops in the vicinity of the low-level shear line and in the easterly airflow on the surface,which results in wide range of severe rainfall with the hourly rainfall intensity higher than 20 mm and lower than 50 mm,and the 24 h rainfall surpassing 100 mm in localized regions.In conclusion,by analyzing the characteristics of the two types of rainstorms in northeastern Guizhou affected by the transverse shear line in the middle and lower reaches of the Yangtze River as well as the similarities and differences of the influencing systems,we have made efforts to reveal the differences and causes of rainstorms,which is expected to help improve the forecasting ability of such rainstorms.