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广东2005年“3·22”强飑线天气过程分析
Dynamic Diagnosis of an Infrequent Squall Line in Guangdong on March 22, 2005
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摘要: 利用地面常规及自动气象站观测、NCEP/NCAR 1°×1°再分析资料和多普勒雷达探测等资料, 对2005年3月22日广东一次近年罕见的强飑线过程进行了天气动力学和中尺度的诊断分析, 对伴随飑线的强风暴区天气系统配置、空间结构特征及其演变特征等作了深入的探讨, 同时计算了强对流天气发生区域的有关物理量, 从中发现了一些有意义的事实, 以求为以后广东春季强对流天气的监测和预警提供一些有益的帮助。Abstract: A dynamic diagnosis and meso-scale analysis of an infrequent squall line on March 22, 2005 in Guangdong is made using the routine observations, automatic weather station data, NCEP/NCAR reanalysis data and Doppler radar images. It's found that the squall line occurs under unstable stratification of environmental conditions and unstable physical mechanism, such as the trough at 500 hPa affecting the region where Guangdong borders Guangxi ahead of the trough at 700 hPa, so the acclivitous trough may be the dynamical trigger mechanism of the squall line's occurrence; the intrusion of the dry and cold air down from the upper troposphere affords the thermal instability field; the westerly jet is overlapped with the low southwest jet over the Guangdong and Guangxi, which brings the strong vertical wind shear, and the squall line develops strongly along the exit area of the low level jet after it is formed at the entrance of the upper jet above the low level jet; in the north and south of the squall line there are many new convection cells which keep building and tend to be combined towards the middle of the bow-shaped echo when the squall line grows; the squall line tends to have a dissy mmetrical structure rather than a symmetrical structure when it weakens, and the comma head and tail of the squall line, which cause disasters, are still growing respectively; the echo's channel of weak reflectivity factor at the rear end of the bow-shaped echo, namely the mesosphere-influx mouth of trough, comes forth, which is a sign to the change when the squall line has turned to dissymmetrical structure from symmetrical structure, and the squall line develops to the most powerful stage; in this process it shows some features such as the bow-shaped echo, the V-shaped mouth of trough, MARC and "long convection line" in front of the squall line. The strong inflow center, velocity convergence zone and small vortex velocity feature from the meridional velocity are also found. It is a good sign to identify the change of multi-cell storms that the long convection line of images occurs and develops all along the squall line; diagnostic analysis shows that the physical measures such as the vertical speed, wet static energy and CAPE can reflect effectively where the squall line has been born and where it has moved to.
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Key words:
- squall line;
- acclivitous trough;
- jet flow;
- long convection line
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图 1 广东2005年3月22日逐时灾害天气落区分布及对应时次飑线位置图
(粗实线代表飑线, 粗虚线范围是飑线减弱后的对流云团, 疏点、横线、斜线、反斜线、竖线和密点区代表的分别是09:00, 10:00, 11:00, 12:00—13:00, 14:00, 15:00—16:00出现灾害天气区域, 小方框点代表观测到冰雹的测站)
Fig. 1 Hourly distribution of severe weather occurrence areas and corresponding locations of squall lines on March 22, 2005
(thick solid lines denote squall lines, while the thick dashed line indicates convective cloud after the squall line weakened, with the sparse dots, horizontal lines, slash lines, backslash lines, upright lines and dense dots indicating areas of severe weather occurrences at 09:00, 10:00, 11:00, 12:00—13:00, 14:00, 15:00—16:00, respectively; the small squares are stations that observed hailstones.)
图 2 2005年3月22日08:00天气系统综合配置图
(粗实线:500 hPa槽线; 粗虚线:700 hPa槽线; 粗箭头代表北方冷空气主体; 小箭头指示850 hPa急流轴位置)
Fig. 2 The composite diagram for synoptic systems at 08:00 on March 22, 2005
(the thick solid line represents trough at 500 hPa, while the dashed one for trough at 700 hPa; the big arrow indicates dominant cold flow from the north and the small arrow is for jet line at 850 hPa)
图 3 2005年3月21日20:00(a) 和22日08:00(b)200 hPa的等风速线、急流位置与强对流天气区
(实线箭头表示200 hPa急流轴, 虚线箭头表示700 hPa急流轴, 阴影区表示22日强对流天气发生区)
Fig. 3 Isotaches at 200 hPa, locations of jet streams (solid line with arrow for 200 hPa while dashed one for 700 hPa) at (a)20:00 on March 21 and (b)08:00 on March 22, 2005 and strong convective occurence areas only for March 22 (shaded area)
图 4 2005年3月21日20:00沿110°E的中高层和对流层低层的ΔT经向剖面图
Fig. 4 Meridional variation of ΔT in upper and lower tropospheres along 110°E at 20:00 on March 21, 2005
图 5 2005年3月22日08:10阳江雷达回波图
(a) 反射率因子，（b) 径向速度，（c)图 5b的分析流场 (仰角：1.5°，距离每圈50 km, 回波在雷达西北方向约150〜200 km处）
Fig. 5 Observations by the Yangjiang radar at 08:10 on March 22, 2005
(a) reflectivity factor, (b) velocity, (c) analyzed flow field corresponding Fig. 5b (elevation:1.5°; the distance between two adjacent circles is 50 km; the echo is observed at 150—200 km northwest to the radar station)
图 6 2005年3月22日09:11阳江雷达回波图
(a) 反射率因子，仰角0.5°, (b) 反射率因子，仰角1.5°, (c) 径向速度，仰角1.5°(距离每圈50 km, 回波在雷达西北方向约100~150km处）
Fig. 6 Observations by the Yangjiang radar at 09:11 on March 22, 2005 reflectivity factor with elevation of 0.5°(a) and 1.5° (b), velocity with elevation of 1.5° (c) (the distance between two adjacent circles is 50 km, the echo is observed at 100-150 km northwest to the radar station)
图 7 2005年3月22日广州雷达回波图
（a)10:57 RCS图，（b) 11:14 VCS图 (方位角：288°，强回波中心距雷达约15 km)
Fig. 7 Observations by Guangzhou radar in the direction of 288° on March 22, 2005
(a) RCS at 10:57, (b) VCS at 11:14 (the center of the strong echo is located in about 15 km from the radar)
图 8 2005年3月22日广州雷达10:57—12:30雷达回波图
(红色箭头线是分析的流线）(a) 10:57, 0.5°仰角，径向速度，（b) 11:32 CR，（c) 12:14, 0.5°仰角, 反射率因子，(d) 12:30, 1.5°仰角，反射率因子，（e) 12:14, 0.5°仰角，径向速度，（f) 12:30, 1.5°仰角，径向速度
Fig. 8 Echo intensity and mean relative velocity of the storm at 10:57-12:30, observed by the Guangzhou radar on March 22, 2005
(the red lines with arrows are analyzed streamlines) (a) 10:57 velocity with elevation of 0.5°, (b) 11:32 CR, (c) 12:14 reflectivity factor with elevation of 0.5°, (d) 12:30 reflectivy factor with elevation of 1.5°, (e) 12:14 velocity with elevation of 0.5°, (f) 12:30 velocity with elevation of 1.5°
图 9 2005年3月22日广州雷达11:26反射率因子图
Fig. 9 Reflectivity factor observed by the Guangzhou Doppler radar at 11:26 on March 22, 2005
图 10 2005年3月22日08:00沿23°N垂直速度的纬向剖面图 (单位:10 hPa·s-l)
Fig. 10 Zonal section of vertical velocity along 23°N at 08:00 on March 22, 2005(unit:10 2hPa·s-1)
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