长生命史飑线在强、弱对流降水过程中的异同点分析

Analyese on Different and Common Points of Long Life Squall Line in Severe,Weak Convection Precipitation Processes

利用常规气象资料、自动站资料、NCEP再分析资料和多普勒雷达资料,对发生在我国中纬度地区不同对流环境下两次长生命史飑线过程的物理机制和中尺度特征进行了分析。结果表明:(1)飑线在近地面层有较强的水汽辐合,但强对流降水过程中的飑线湿层深厚,水汽辐合的层次更为深广、强度更强,存在较低的抬升凝结高度。(2)高层强冷平流与低层暖平流的叠加是飑线的共同特征之一;不同之处在于弱对流降水过程中飑线不稳定层结的建立更多地依靠高层冷平流的作用,有更高的温度直减率,具有弱降水超级单体的一些特征;强对流降水过程中飑线低层暖平流的加强也是造成大气不稳定的重要原因,θse在中层呈现出湿中性层结特征,存在更大的热力不稳定度,是典型的强降水超级单体特性。(3)长生命史飑线的发展离不开强环境风垂直风切变;强对流降水过程中垂直风切变主要是风速随高度变化而产生的,弱对流降水过程中垂直风切变主要表现为风向随高度的变化。(4)飑线沿着出流边界和引导气流方向移动。(5)飑线在雷达回波上的共同点:都出现典型弓形回波,减弱的标志亦是阵风锋逐渐远离回波主体,弓形回波逐渐断裂,强回波后侧的层状云回波面积开始增大;不同点在于弓形回波的演变方式不同,弱对流降水过程中的弓形回波有超级单体风暴的典型结构,而强对流降水过程中弓形回波的形成是由强降水超级单体的发展而来,单体结构明显不同于经典超级单体中非降水或弱降水超级单体。(6)速度场上低层存在着径向速度的大值区,中低层有辐合,并伴有中气旋存在,中层存在明显的MARC(Mid-Altitude Radial Convergence)。1km高度以下的径向速度大值区、MARC和中气旋对地面灾害性大风有提前预警作用。

Based on the conventional observation data,automatic weather station data,NCEP 1°×1° reanalysis data and Doppler radar data,the physical mechanisms and mesoscale features of two long life squall lines under the different convection environments have been researched.The main conclusions are as follow：（1） Squall line has strong moisture convergence in surface layer;in severe convection precipitation process,squall line usually has deeper wet layer,stronger and more wider vapor convergence,and the lifting condensation level is lower.（2） One of the common features of squall line is that the strong cold advection in the upper level superpose on the warm advection in the low level,which is of difference in weak convection precipitation process,the establishment of unstable stratification mainly relates to the cold advection in the upper level,the lapse rate of temperature is higher,these are some characteristics of weak precipitation supercell.But in severe convection precipitation process,strengthening of the warm advection in the low level also is the important reason of unstable stratification,θse has the humid neutral stratification characteristic in the middle level and there is greater thermal unstable,which is of the typical characteristic of severe precipitation supercell.（3） Long life squall line all develop with the strong vertical wind shear;the vertical wind shear mainly cause by wind speed varying with height in severe convection precipitation process,and by wind direction varying with height in weak convection precipitation process.（4） Squall line all move along the direction of outflux boundary and leading flow.（5） The common points of squall line on the radar echo are that they all have typical bow echo,the bow echo recedes when the gust front is away from the storm cell and the area of stratiform cloud echo increases.Squall line of Doppler radar radial velocity associate with the development of the high area of meridional speed in the low level,MARC in middle level and the large range middle convergence accompany with mesocyclone developping.The different ponit is the evolution of bow echo： In weak convection precipitation process the bow echo has the typical structure of supercell,but in severe convection precipitation process the bow echo develops with severe precipitation supercell,the structure is markedly different from classical supercell or weak precipitation supercell.（6） The high area of meridional speed under 1 km height,MARC and mesocyclones can be early-warning of disastrous winds on the surface.