Analysis of Organizational Modes of Mesoscale Convective Systems Associated with Extreme Precipitation in Shanwei During Annually First Rainy Seasons
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摘要: 利用2013—2022年天气雷达、站点观测数据及ERA5再分析资料等,提炼出造成广东汕尾前汛期极端强降水的中尺度对流系统(MCS)组织形态的类型,并分析其与强降水的关系。结果表明:(1) 造成汕尾前汛期极端强降水的MCS可分为4类:尾随层状降水(TS)、准静止后向建立(BB)、断裂线状(BL)和非线状(NL),且存在不同类型MCS先后演变的情况。(2) BB和BL均移动缓慢,其中BB具有后向传播特征,BL为断裂的线状回波;TS则具有一定的移速,强对流回波带位于系统移动方向前方。(3) MCS多在5月中旬至6月上旬触发于广东惠州至海丰沿海,影响时间多始于夜间至清晨,下午至上半夜发展最旺盛,其中BB影响时间和成熟期最长。(4) 整体而言,各类型MCS影响期间导致的平均小时雨量大值区集中在海丰中部,其中BL导致的小时雨强大值区范围最广。另外BB有4次出现中尺度涡旋特征,且通常能导致最大的短时雨强。(5) 各类型MCS个例均为南支槽或弱波动东移影响,其中TS伴有切变线和锋面南压,BB和BL均出现在暖区暴雨过程中。Abstract: Utilizing weather radar data, observational data from surface stations, and ERA5 reanalysis data from 2013 to 2022, this study analyzed the organizational modes of mesoscale convective systems (MCSs) associated with extremely heavy rainfall events in Shanwei during annually first rainy seasons and their relationship with strong precipitation. The results are as follows. (1) The MCSs can be categorized into four categories: trailing stratiform (TS), back building (BB), broken line (BL), and nonlinear (NL), with some cases exhibiting transitional evolution between different MCS types. (2) Both BB and BL systems moved slowly. BB systems exhibited backward propagation characteristics, while the BL systems were characterized by discontinuous line echoes. TS systems moved at a moderate speed, with strong convective echo bands located ahead of the systems'direction of motion. (3) These MCSs predominantly initiated along the coast from Huizhou to Haifeng between mid-May and early June, with their impact typically starting from nighttime to early morning. The most vigorous development usually occurred from the afternoon to midnight, with BB systems having the longest duration of impact and maturity phase. (4) The maximum hourly rainfall during MCS events was consistently observed in central Haifeng. BL systems produced the most extensive area of intense precipitation. Moreover, BB systems displayed mesoscale vortex features in four cases and tended to result in the strongest short-duration rainfall. (5) All types of MCSs were influenced by either south branch troughs or weak disturbances. TS systems were accompanied by shear lines and frontal systems, while BB and BL systems were associated with warm-sector heavy rainfall events.
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表 1 2013—2022年前汛期汕尾极端强降水开始影响日期和MCS类型
序号 日期 MCS类型 序号 日期 MCS类型 1 2013/04/30 BB 16 2015/05/20 TS 2 2013/04/30 TS 17 2018/05/07 BB 3 2014/05/16 BL 18 2018/05/07 TS 4 2014/05/16 TS 19 2018/06/22 BB 5 2014/05/16 BL 20 2020/05/21 NL 6 2014/05/18 NL 21 2020/06/08 BB 7 2014/05/19 BB 22 2021/05/31 BB 8 2014/05/19 TS 23 2021/05/31 BL 9 2014/05/21 BB 24 2022/05/12 BL 10 2014/05/22 BL 25 2022/05/12 BB 11 2014/05/22 TS 26 2022/06/03 BB 12 2014/05/22 BB 27 2022/06/07 BB 13 2015/05/19 TS 28 2022/06/07 TS 14 2015/05/19 BL 29 2022/06/12 BB 15 2015/05/20 BB 注:NL(Non Line)为非线状型,TS(Trailing Stratiform)为尾随层状型,BB(Back Building)为准静止后向建立型,BL(Broken Line)为断裂线状型。 表 2 2013—2022年前汛期汕尾极端强降水过程线状MCS平均影响时长及成熟阶段时长
MCS类型 出现次数 平均影响时长/h 平均成熟阶段时长/h BB 13 8.3 5.2 TS 8 4.5 2.5 BL 6 5.3 2.8 表 3 各类型线状MCS的探空物理参数和雷达回波参数的平均值
参数 TS BB BL 整体平均 CAPE/(J·kg-1) 1 120.3 1 023.1 1 260.7 1 104.7 925 hPa比湿/(g·kg-1) 18.8 18.9 19.4 19.0 0 ~ 1 km风切变(m·s-1) 4.5 3.3 3.5 3.7 0 ~ 3 km风切变(m·s-1) 8.7 8.5 8.2 8.5 0 ~ 6 km风切变(m·s-1) 9.9 10.2 9.4 9.9 50 dBZ伸展高度/km 5.1 5.0 5.3 5.1 最强反射率因子/dBZ 58.8 58.1 56.7 58.0 VIL/(kg·m-2) 33.8 32.3 31.7 32.6 中尺度涡旋次数 0 4 0 0.1 -
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