Investigation of Derechos in China: Spatiotemporal distribution,environmental characteristics,and morphology of Derechos producing convective systems
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摘要: 基于2002—2019年高空、地面常规观测资料,卫星云图,部分新一代天气雷达单站资料以及2009年以后的中国雷达拼图资料,采用个例筛选与统计、动态合成分析、层次聚类和雷达图分析等方法,对发生在中国的大范围雷暴大风事件(Derechos)的时空分布、环境背景和对流系统形态特征进行了分析。结果表明:(1)Derechos事件主要发生在华北、华东、江南和华南地区,高频区有明显的季节变化,春季到夏季先向北移动后向南移动;Derechos事件主要发生在3—8月,6月频率最高,8月最低;造成Derechos的对流风暴多在正午前后生成,而Derechos事件多开始于午后到前半夜。(2)中国Derechos事件环境参数主要特征为:对流有效位能(CAPE)分布50%分位(中位数)为1420 J/kg,代表深层风垂直切变的0—6 km风矢量差50%分位数为18.0 m/s,对流下沉有效位能(DCAPE)的50%分位值为1090 J/kg。(3)Derechos事件环流背景的天气流型配置分为副高边缘型、弱槽型、高空干冷平流强迫型和强槽型,强槽型出现的频次最高,高空干冷平流强迫型出现的频次最低。(4)Derechos事件中最强对流大风产生时段的对流系统形态统计显示,出现频率由高到低分别为飑线、多单体风暴簇、超级单体或超级单体复合体。Abstract: Based on the 36 Derechos that occurred in China during 18 years from 2002 to 2019, a study on the spatiotemporal distribution and environmental characteristics of Derechos as well as the morphology of Derechos producing convective systems have been conducted using proximity soundings, surface observations, satellite images, single Doppler weather radar data, and weather radar mosaics data. The results are as follows. (1) Derechos mainly occur in the eastern half of China, including North China, East China, South China, and regions to the south of the Yangtze River. The regions of high occurrence frequency show remarkable seasonal variation, which is manifested as the northward movement during the first phase and the southward movement during the second phase from spring to summer. Derechos activity has significant seasonal changes. They mainly occur from March to August with the highest frequency in June and the lowest in August. The convective systems producing the Derechos tend to initiate around noon, while the Derechos themselves tend to occur between mid-afternoon and early midnight. (2) The main characteristics of environmental parameters of Derechos in China are as follows: The 50th percentile of CAPE is 1420 J/kg, the 50th percentile of the 0—6 km vertical shear is 18.0 m/s, the 50th percentile of DCAPE is 1090 J/kg. (3) The weather pattern of Derechos can be divided into the following four types: The subtropical high periphery type, the weak trough type, the high level dry-cold advection forced type and the strong trough type, among which the strong trough type has the highest frequency and the high level dry-cold advection forced type has the lowest frequency. (4) During the period when the maximum wind gust occurs, the most frequent convective storm type is squall line, the second frequent storm type is multi-cell cluster storm and the third frequent storm type is supercell storm.
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图 2 叠加红外云图的2005年5月5日Derecho事件影响范围和探空站分布 (黄色实线代表Derecho事件范围,红色圆点代表探空站位置;a. 08时,b. 11时)
Figure 2. Composite graph of infrared cloud image,Derecho event scope and sounding stations distribution in 5 May 2005 (the light yellow solid line shows the range of the Derecho event,the red dots indicate the positions of sounding stations;a. 08:00 BT,b. 11:00 BT)
图 8 不同天气流型500 hPa位势高度 (黑色实线,单位:gpm)、温度 (红色虚线,单位:℃) 及大风落区 (灰色阴影);横坐标为相对原点 (Derecho起始位置) 的经度,纵坐标为相对原点 (Derecho起始位置) 的纬度 (a. 副高边缘型, b. 弱槽型, c. 高空干冷平流强迫型, d. 强槽型)
Figure 8. Four types of weather pattern shown by 500 hPa geopotential height (black solid lines,unit:gpm),temperature (red dashed lines,unit:℃) and the Derechos strong wind regions (areas shaded in gray);the x-coordinate represents the longitude relative to the origin (Derecho starting position),and the y-coordinate represents the latitude relative to the origin (Derecho starting position)(a. subtropical high periphery type,b. weak trough type,c. high level dry-cold advection forced type,d. strong trough type)
图 9 Derechos个例对流系统形态及演变 (2002年8月24日合肥SA型天气雷达0.5°仰角反射率因子:(a1) 12时30分,(a2) 14时;b1. 2005年3月22日09时32分广州SA型天气雷达0.5°仰角反射率因子,b2. 2005年3月22日15时02分龙岩SA型天气雷达0.5°仰角反射率因子;2009年6月3日商丘SB型天气雷达0.5°仰角反射率因子:(c1) 20时50分,(c2) 23时28分;相邻圈间隔50 km)
Figure 9. Morphology and evolution of Derchos producing convective systems (Hefei SA radar 0.5° elevation reflectivity at 12:30 BT (a1) and 14:00 BT (a2) 24 August 2002;Guangzhou SA radar 0.5° elevation reflectivity at 09:32 BT (b1) and Longyan SA radar 0.5° elevation reflectivity at 15:02 BT (b2) 22 March 2005;Shangqiu SB radar 0.5° elevation reflectivity at 20:50 BT (c1) and 23:28 BT (c2) 3 June 2009)
表 1 三种Derechos识别标准
Table 1. Three identification criteria of Derechos
JH87标准 BM98标准 Coniglio2004a标准 区域风灾报告密集,风灾由对流性系统产生;对流阵风超过26 m/s,区域长轴长不低于400 km 同JH87标准 同JH87标准 事件发生不是随机的,随时间演变分布 同JH87标准 同JH87标准 阵风灾害事件之间的时间间隔不超过3 h 阵风灾害事件之间的时间间隔不超过2 h 阵风灾害事件之间的时间间隔不超过2.5 h 区域中至少有3个事件发生点,每个点之间相隔64 km及以上,并且造成了F1级损害或者对流阵风超过33 m/s 不采用JH87中此条标准 中等级别大风事件与JH87相同;高级别大风事件定义为区域中至少有3次阵风超过38 m/s或根据房屋、树木受损情况估计的相同级别的阵风风速,并且3次事件中至少2次必须发生在此次大风过程中中尺度对流系统的某个生命阶段 由地面气压场和风场所反映的中尺度对流系统必须具有空间和时间连续性 (与大风)相关的中尺度对流系统必须具有时、空连续性,报告的相邻(连续)大风间距不超过2个经度或纬度 (与大风)相关的中尺度对流系统必须具有时、空连续性,且必须在阵风范围中,并距报告的其他阵风不超过200 km 通过核验现有的雷达数据,以确认破坏性大风区与同一个中尺度对流系统移动路径重合 通过将对应时刻的事件发生位置绘制在地图上,以确认灾害大风区与同一个中尺度对流系统移动路径重合 同JH87标准 表 2 环境参数特征值
Table 2. Eigenvalues of the distribution of environmental parameters
物理量 最小值 25%分位 中位数 平均值 75%分位 最大值 850—500 hPa温差(°C) 19.0 25.0 26.6 26.9 29.1 37.0 700—500 hPa温差(°C) 12.0 15.8 17.0 17.4 18.9 25.0 抬升凝结高度(km) 0.0 0.5 1.0 1.1 1.6 2.8 可降水量(mm) 7 25 35 34 45 62 850—500 hPa相当位温差(°C) −10.8 3.1 12.0 10.5 16.0 31.4 CAPE(J/kg) 0 270 1140 1330 2130 3890 CAPE(Tv) (J/kg) 0 460 1420 1590 2490 4290 DCAPE(J/kg) 10 840 1090 1060 1320 1820 地面露点温度(°C) −1.0 15.2 19.0 17.8 22.0 27.0 地面温度露点差(°C) 0.0 4.0 8.0 8.5 12.0 25.0 1.5 km温度露点差(°C) 0.0 1.8 5.0 7.1 10.0 48.0 3—6 km平均温度露点差(°C) 1.8 10.0 14.5 14.8 19.0 36.5 3—6 km最大温度露点差(°C) 3.4 18.8 25.0 26.4 34.5 48.0 0—3 km风垂直切变(m/s) 0.3 8.0 11.0 12.2 16.0 29.2 0—6 km风垂直切变(m/s) 5.0 13.0 18.0 19.8 26.0 43.1 3—6 km风垂直切变(m/s) 0.0 5.2 8.3 10.1 14.7 35.2 0—10 km风垂直切变(m/s) 1.6 16.1 25.4 29.2 42.4 74.2 -
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