豫北一次局地雹暴天气的预警特征和触发机制

利用常规气象观测、多普勒雷达、卫星资料和区域自动站观测资料及NCEP再分析资料,对2011年6月11日豫北局地强对流天气的预报预警特征和触发机制进行分析。结果表明：局地强对流天气是在东北冷涡背景下产生的,高低层中尺度影响系统(槽、切变线、大风速轴)交汇处右侧是强对流发生潜势区。局地强对流天气发生前,CAPE较大,0-6 km垂直风切变达到中等偏强,有利于超级单体的形成和发展。高空冷平流南侵、低层暖平流北上,有利于大气对流不稳定度进一步加大。中-β尺度强对流云团在东北冷涡槽底后部形成,其发展演变对局地强对流天气预报预警有参考意义。强对流回波经历了细胞状、带状发展期和块状减弱期。回波带南侧形成的超级单体造成了局地强风雹天气,冰雹发生时伴有“三体散射”现象。冷空气和地面辐合线是强对流天气的主要触发机制;地面辐合线对强对流天气还有提示作用。     

一次强飑线内强降水超级单体风暴的单多普勒雷达分析

文中利用位于福建建阳新一代S波段多普勒天气雷达资料和探空、地面观测资料,对2003年4月12日07-09时发生在建阳附近的一次强降水超级单体风暴进行了分析.天气分析显示,风暴发生于地面冷锋北侧、低层高湿、中等对流不稳定(1601 J/kg)和强风切变(0-5 km,22 m/s)环境,总理查逊数为16,同典型的强降水超级单体生成环境相当接近.雷达回波分析揭示,风暴发生在一强飑线系统的前沿,初期为一普通单体,随后逐渐发展成为弓状并发生分裂,分裂后风暴移动方向左侧单体逐渐减弱.而右侧的单体发展成为超级单体,持续时间约为1 h.在强降水超级单体成熟期,其移动前侧的低层反射率因子出现明显的钩状回波,中层反射率则显示在宽广的反射率高值区(>60 dBz)内存在有界弱回波区,强度大于40 dBz.沿入流方向穿过最强回波位置的反射率因子也呈现典型的回波悬垂和有界弱回波区.相应的中低层径向速度场显示在钩状回刎波附近的强降水区中存在一个强烈的中气旋,其起源于中层3.5-5 km,随后向上、下发展,最大旋转速度达到24 m/s,持续时间达1 h.由GBVTD方法分析,中气旋成熟时(08:33 UTC)轴对称环流结构显示,轴对称切向风分布在中层接近兰金涡旋模型,最大轴对称切线风位于高度4-5 km,离气旋中心约3 km,强度约20 m/s.4 km高度以下为气旋式辐合,气旋中心为上升运动.至4-7 km以旋转为主,在最大切向风半径以内为外流,以外为内流,相应的在最大风速半径处伴随较强的辐合和上升运动,7 km以上则为辐散对应的出流.此结构同经典超级单体内的中气旋结构相当一致.此外.风暴结构同Moller(1994)提出的中纬度强降水超级单体风暴的特征非常相似.但演变过程却明显不同,是由普通单体形成弓状回波,弓状回波分裂后沿移动方向右侧的单体发展成为强降水超级单体.     

Single-Doppler Radar Observations of a High Precipitation Supercell Accompanying the 12 April 2003 Severe Squall Line in Fujian Province

In this study,single Doppler radar data were used to examine the structure and evolution of a high precipitation(HP) supercell embedded in a cold front near Jianyang,Fujian Province on 12 April 2003.The synoptic environment was characterized by high humidity at low levels,moderate CAPE(convective available potential energy;1601 J kg~(-1)),moderate wind shear(22 m s~(-1) in 0-5 km),and veering of the horizontal winds with height,similar to those HP supercells previously observed in midlatitudes.In additio...     

2004年4月29日常德超级单体研究

利用常德和长沙多普勒天气雷达资料和常规资料,对2004年4月29日发生在湖南安乡且产生了10 cm直径降雹和广泛8级大风的超级单体风暴进行了详细分析.该超级单体风暴发生在西南高空急流和西南南低空急流的交汇区域,加强的热力不稳定趋势和较大的垂直风切变条件非常有利于超级单体的产生.超级单体风暴呈现出典型的钩状回波,钩状回波位于该超级单体风暴移动方向的右后侧,从低层一直扩展到将近6 km高度;同时出现了指示存在大冰雹的三体散射回波.此次超级单体风暴成熟阶段中气旋的最大旋转速度为24 m·s-1,属于强中气旋,相应的垂直涡度为1.6×10-2 s-1.反射率因子的垂直剖面显示该超级单体风暴具有一个宽大的有界弱回波区(穹窿),其水平尺度超过10 km,垂直扩展超过4 km.在有界弱回波区之上,是一个强度超过70 dBZ的反射率因子核区,其中心高度为9 km,展现出典型的强烈超级单体雹暴结构.超级单体风暴在演变过程中经历了3次分裂过程.     

Single-Doppler Radar Observations of a High Precipitation Supercell Accompanying the 12 April 2003 Severe Squall Line in Fujian Province

In this study, single Doppler radar data were used to examine the structure and evolution of a high precipitation (HP) supercell embedded in a cold front ne㎡ar Jianyang, Fujian Province on 12 April 2003. The synoptic environment was characterized by high humidity at low levels, moderate CAPE (convective available potential energy; 1601 J kg?1), moderate wind shear (22 m s?1 in 0-5 km), and veering of the horizontal winds with height, similar to those HP supercells previously observed in midlatitudes. In addition, the calculated bulk Richardson number was only 16, suggesting favorable environmental conditions for supercell development. The documented storm was located at the leading edge of a squall line. It was initiated from a single cell at 0732 UTC. It evolved into a bow shape gradually, and then split into two separate storms along the storm motion direction through the apex of the bow echo. The left-moving storm dissipated rapidly,but the right-moving storm strengthened and evolved into an HP supercell, lasting for more than 1 h. The radar reflectivity of the HP supercell during its mature stage showed a typical low-level hook echo at the front flank of the storm with its maximum reflectivity beyond 70 dBZ. Above the hook echo, an elevated maximum reflectivity core accompanied by a bounded weak-echo region (BWER) and a down-shear echo overhanging aloft were clearly identified. The elevated BWER, marked by 40-50-dBZ reflectivity values, was surrounded by values of 60-70 dBZ. A well-defined mesocyclone lasted about 1 h and was collocated with the low-level WER and middle-level BWER. The radar-estimated time-height profiles of mesocyclone rotational velocity and diameter indicated that this mesocyclone formed initially at middle level, then deepened and strengthened rapidly with the vertical depth deeper than 8 km and rotational velocity stronger than 24 m s-1 at the mature stage, and later decayed rapidly. The GBVTD (ground-based velocity track display)-derived primary circulation showed that the maximum tangential wind of the mesocyclone appeared at middle level (3-5 km) with a value of about 20 m s-1. The mean radial wind field was characterized with a low-level inflow below 4 km, and accompanied by stronger updraft near the mesocyclone center. Between 4 and 7km, the tangential wind profile resembled a Rankine combined vortex with the radius of maximum wind (RMW) at 3 km, and there was outflow/inflow inside/outside of the RMW. Correspondingly, the vertical velocity indicated a stronger updraft at the RMW and a weak downdraft inside the RMW. Above 7 km, the outflow strengthened and extended outside the RMW. In summary, the reflectivity structures of the storm and the accompanying mesocyclone were similar to those midlatitude HP supercells proposed in Miller's paper in 1994. However, the evolution of the HP supercell, including its three stages: ordinary storm, bow echo, and storm splitting, was quite different from those documented before.     

对丽水强对流天气过程的中尺度分析和预警启示

通过对强对流过程天气背景、物理量诊断分析,发现西南暖湿气流致使大气增温增湿和能量的积聚,大气处于不稳定状态;利用高频次、高分辨率的新一代天气雷达产品进一步分析,发现雷达基本反射率图像中显现出风暴的"穹窿"和BWER等结构特征;对流单体质心反射率强度、高度和冰雹概率均有陡增的现象.大气中的暧平流、高低空辐散、辐合场相配合导致垂直运动强烈发展并维持,促成了强对流天气过程.