| 潘玉洁,赵坤,潘益农. 2008. 一次强飑线内强降水超级单体风暴的单多普勒雷达分析[J]. 气象学报, 66(4):621-636, doi:10.11676/qxxb2008.059 |
| 一次强飑线内强降水超级单体风暴的单多普勒雷达分析 |
| Single -Doppler radar observation of a heavy precipitation supercell on a severe squall line |
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| DOI：10.11676/qxxb2008.059 |
| 中文关键词: 强降水超级单体，钩状回波，中气旋 |
| 英文关键词:HP supercell, Hook echo, Bounded weak echo (BWER), Mesocyclone |
| 基金项目:国家自然基金(40505004)；关键区强对流天气触发、维持机制及其可预报性(GYHY200706033) |
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| 中文摘要: |
| 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。 |
| 英文摘要: |
| The single Doppler radar data of Jianyang, Fujian Province were used to analyze the structure and evolution of a heavy precipitation (HP) supercell in the north side of a cold front near Jianyang during 07:00-09:00 UTC 12 April 2004. The synoptic environment was characterized by high humidity in low-levels,moderate CAPE (Convective Available Potential Energy,1601 J/kg), moderate wind shear (22 m/s， over 0-5 km) and the veering of wind with height, which are similar to those of HP supercell previously observed in mid-latitudes. In addition, the calculated bulk Richardson number is only 16, which also suggests the environmental conditions favorable for supercell development. The Doppler radar analysis shows that the storm took place at the leading edge of a squall line, developed initially from an ordinary storm, and then evolved gradually into a bow shape. Subsequently, it split up into two separate storms along the storm motion direction through the apex of the bow echo. The storm in the left flank dissipated quickly, however the right storm strengthened and evolved into a HP supercell and lasted more than one hour. The radar reflectivity of the HP supercell at its mature stage displayed a typical low-level hook echo at the front flank of the stormand the maximum reflectivity was beyond 70 dBz. Above the hook echo, an elevated maximum reflectivity core, subtle bounded weak-echo region (BWER) and downshear echo overhang aloft can be clearly identified. The elevated BWER with the reflectivity of 40-50 dBz was surrounded by values of 60-70 dBz. Corresponding storm relative velocity data showed a well defined, deep layered (above 7 km) mesocyclone coincident with the low-level WER and middle-level BWER. The radar-estimated time-height cross section of mesocyclone rotational velocity and couplet diameter indicates that this mesocyclone formed initially at middle level, then deepened and strengthened rapidly into mature stage with a vertical depth more than 8 km and a maximum rotation velocity more than 24 m/s, and later decayed rapidly. It lasted for about 1 hour. The GBVTD derived primary circulation shows the maximum tangential wind of the mesocylone laid at middle level (3-5 km) with a maximum about 20 m/s. The mean radial wind field was characterized with a low-level inflow below 4 km, accompanied a stronger updraft near the mesocyclone center. Between 4-7 km, the tangential wind profile resembled that of a Rankine combined vortex with the maximum radius of wind (RMW) at 3 km. The mean radial wind field was characterized with a low-level outflow within the RMW and inflow outside the RMW respectively. Correspondingly, the vertical velocity indicated a stronger updraft at the RMW and weak downdraft inside the RMW. Above 7 km, the outflow strengthened and extended outside the RMW. In a summary, the reflectivity structure of storm and its accompanied mesocyclone are very similar with those of mid-latitude HP supercell proposed by Miller 1994. However, its life cycle included three stages: ordinary storm, bow echo and storm split, which is quite different from those recorded before. |
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