THE SPATIAL AND TEMPORAL DISTRIBUTION OF CHINESE TORNADOS AND THEIR CHARACTERISTICS ANALYSIS OF ENVIRONMENTAL PHYSICAL VARIATIONS
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摘要: 利用2004—2012年《中国气象灾害年鉴》和CFSR再分析资料,研究中国龙卷的时空分布以及三个龙卷频发区的环流背景场和环境物理量特征,并比较他们之间的区域差异。结果表明:中国龙卷多发生于春夏季,午后傍晚较多,江苏和广东等平原地区出现龙卷概率最高。龙卷临近时,“江苏及其邻近地区”位于500 hPa槽前,850 hPa上有西南急流,造成了较强的低层垂直风切变;“广东及其邻近地区”在龙卷发生前地面对流有效位能均值达997.3 J/kg,0~1 km螺旋度均值达91 m2/s2,层结不稳定,动力抬升强;“东北地区”受深厚东北冷涡控制,整层水汽含量低,中低层比湿均值小于10 g/kg。通过比较环境物理量平均场的分布特征发现:螺旋度、垂直风切变、能量螺旋度指数和强龙卷参数对分析龙卷发生有很好的指示意义。“东北地区”对流有效位能和比湿均值远低于“江苏及其邻近地区”和“广东及其邻近地区”,但高低空的温度直减率大、中低层的垂直风切变强,该地区也会产生龙卷。Abstract: Using data of Chinese Meteorological Disasters Yearbook for 2004 to 2012 and CFSR reanalysis, this paper analyzes the spatial and temporal distribution characteristics of tornadoes in China, circulation background field and the characteristics of environmental physical variations in three tornado-prone regions, and compares their regional differences. The results showed that tornadoes occurred most frequently in spring and summer, and in the afternoon and at dust. Probabilities of tornado occurrence over plains in Jiangsu and Guangdong are the highest. When tornadoes are approaching, Jiangsu and its adjacent regionsare located before a trough at 500 hPa level, and a 850 hPa southwest jet leads to a strong low-level vertical wind shear; the mean CAPE value of Guangdong and its adjacent regions preceding to tornado events is 997.3 J/kg and the mean 0~1 km helicity value is 91 m2/s2, indicating stratification instability and strong dynamic lifting. Northeast China is controlled by a deep Northeast cold vortex, the moisture content of the whole layer is low, and the mean specific humidity value in the middle and lower atmosphere is lower than 10 g/kg. By comparing the distribution characteristics of the mean environmental physical variations field, it is demonstrated that helicity, vertical wind shear, EHI and STP are good indicators to tornado occurrence. The mean CAPE and helicity values of Northeast Chinaare far lower than those of the Jiangsu and its adjacent regions and Guangdong and its adjacent regions.With higher upper and lower-level lapse rates and strong middle and lower-level vertical wind shear, however, there is also possibility for tornado occurrence.
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Key words:
- tornado /
- environmental parameter /
- spatial and temporal distribution /
- CAPE /
- helicity
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表 1 强天气参数说明
参数 公式 公式说明 物理意义 对流有效位能
(CAPE)$\int_{{Z_f}}^{{Z_n}} {g\left( {\frac{{{T_{v,{\rm{parcel}}}} - {T_{v,env}}}}{{{T_{v,env}}}}} \right)} {\rm{d}}z$ Zf是自由对流高度,Zn是平衡层, Tv, parcel是气块虚温,Tv, env是环境虚温 表征空气不稳定性 对流抑制能量
(CIN)$\int_{{Z_b}}^{{Z_f}} {g\left( {\frac{{{T_{v,{\rm{parcel}}}} - {T_{v,env}}}}{{{T_{v,env}}}}} \right)} {\rm{d}}z$ Zb是大气底部高度,Zf是自由对流高度, Tv, parcel是气块虚温,Tv, env是环境虚温 表征大气底部的气块达到自由对流高度需要的能量 风暴相对螺旋度
(SRH)$\int {\left( {\overrightarrow {{V_h}} - \overrightarrow C } \right)} \cdot \nabla \times \overrightarrow {{V_h}} {\rm{d}}z$ Vh为气块水平风速,C为风暴移动速度 对流运动中环境空气到气块的涡度转变 抬升凝结高度
(LCL)$123\left( {{T_0} - {T_d}} \right)$ T0和Td分别为地面气温和露点 粗略估算云底高度 能量螺旋度指数
(EHI)$\frac{{{\rm{CAPE}} \cdot {\rm{SRH}}}}{{160\;000}}$ CAPE和SRH分别为对流有效位能和风暴相对螺旋度 把浮力能和动力参数有效结合起来 强龙卷参数
(STP)$\begin{array}{l} \left( {\frac{{sb{\rm{CAPE}}}}{{1500}}} \right) \times \left( {\frac{{2000 - sb{\rm{lcl}}}}{{1000}}} \right)\\ \quad \quad \times \left( {\frac{{{\rm{SRH}}}}{{150}}} \right)\left( {\frac{{{\rm{BWD}}}}{{20}}} \right) \end{array}$ sbCAPE为地面对流有效位能,sblcl为地面抬升凝结高度,SRH为风暴相对螺旋度,BWD是近地面的风切变 强龙卷参数STP常被美国业务上用来预报龙卷发生的可能性,当STP大于1时,易发生EF2及以上的强龙卷 表 2 各区域龙卷发生前最近一时次的热力学合成变量
地区 对流有效位能
/(J/kg)对流抑制能
/(-J/kg)925~850 hPa
温度直减率
/(K/(100 hPa))850~700 hPa
温度直减率
/(K/(100 hPa))925~700 hPa
温度直减率
/(K/(100 hPa))925~500 hPa
温度直减率
/(K/(100 hPa))均值 置信
区间均值 置信
区间均值 置信
区间均值 置信
区间均值 置信
区间均值 置信
区间江苏及其邻近 571.1 449~692 72 84~61 5.5 5.2~5.8 6.0 5.8~6.2 5.9 5.6~6.1 6.6 6.4~6.7 广东及其邻近 997.3 874~1 119 46 61~31 4.9 4.5~5.3 5.7 5.5~5.9 5.4 5.2~5.7 6.4 6.3~6.5 东北 158.6 123~194 55 85~24 5.6 5.2~6.0 7.1 6.9~7.2 6.6 6.4~6.8 7.1 7.0~7.2 表 3 各区域龙卷发生前最近一时次的动力学合成变量
地区 0~1 km螺旋度/(m2/s2) 925~850 hPa垂直风
切变/(m/s)850~700 hPa垂直风
切变/(m/s)925~700 hPa垂直风
切变/(m/s)均值 置信区间 均值 置信区间 均值 置信区间 均值 置信区间 江苏及其邻近 66 58~73 1.9 1.5~2.2 2.5 1.8~3.1 4.2 3.7~4.7 广东及其邻近 91 84~98 2.6 2.0~3.2 3.2 2.6~3.8 5.5 4.7~6.3 东北 99 87~111 3.3 2.7~3.9 2.7 2.1~3.4 5.3 4.6~6.1 表 4 各区域龙卷发生前最近一时次的水汽合成变量
地区 抬升凝结高度/gpm 925 hPa比湿/(g/kg) 850 hPa比湿/(g/kg) 700 hPa比湿/(g/kg) 600 hPa比湿/(g/kg) 均值 置信区间 均值 置信区间 均值 置信区间 均值 置信区间 均值 置信区间 江苏及其邻近 462 317~606 14.0 13.1~14.9 12.0 11.1~12.9 7.8 7.2~8.4 5.2 4.6~5.9 广东及其邻近 412 353~471 14.2 13.6~14.7 12.2 12.0~12.4 7.9 7.7~8.4 5.2 4.9~5.5 东北 1 092 844~1 340 10.0 9.3~10.7 8.5 7.9~9.0 5.7 5.5~5.8 3.2 3.0~3.5 -
[1] KELLY D L, SCHAEFER J T, MCNULTY R P, et al. An augmented tornado climatology[J]. Mon Wea Rev, 1978, 106(8): 1 172-1 183. [2] DOSWELL Ⅲ C A, BURGESS D W. On some issues of United States tornado climatology[J]. Mon Wea Rev, 1988, 116(2): 495-501. [3] DAVID C L. A study of upper air parameters at the time of tornadoes[J]. Mon Wea Rev, 1976, 104(5): 546-551. [4] GRAMS J S, THOMPSON R L, SNIVELY D V, et al. A climatology and comparison of parameters for significant tornado events in the United States[J]. Wea Forecast, 2012, 27(1): 106-123. [5] ROMERO R, GAYà M, DOSWELL Ⅲ C A. European climatology of severe convective storm environmental parameters: A test for significant tornado events[J]. J Atmos Res, 2007, 83(2): 389-404. [6] GRAMS J S, THOMPSON R L, SNIVELY D V, et al. A climatology and comparison of parameters for significant tornado events in the United States[J]. Wea Forecasting, 2012, 27(1):106-123. [7] GRüNWALD S, BROOKS H E. Relationship between sounding derived parameters and the strength of tornadoes in Europe and the USA from reanalysis data[J]. J Atmos Res, 2011, 100(4): 479-488. [8] 范雯杰, 俞小鼎.中国龙卷的时空分布特征[J].气象, 2015, 41(7):793-805. [9] YAO Y Q, YU Z D, ZHANG Y J, et al. Climate analysis of tornadoes in China[J]. J Atmos Res, 2015, 29(3): 359-369. [10] 王沛霖.珠江三角洲春季龙卷发生的环境条件[J].热带气象学报, 1996, 12(1): 60-65. [11] 郑永光, 周康辉, 盛杰, 等.强对流天气监测预报预警技术进展[J].应用气象学报, 2015, 26(6): 641-657. [12] 李彩玲, 杨宇声, 郑启康, 等.一次台风暴雨中的龙卷风天气[J].广东气象, 2007, 29(3): 26-29. [13] 张晰莹, 吴迎旭, 张礼宝.利用卫星、雷达资料分析龙卷发生的环境条件[J].气象, 2013, 39(6): 728-737. [14] 俞小鼎, 郑媛媛, 廖玉芳, 等.一次伴随强烈龙卷的强降水超级单体风暴研究[J].大气科学, 2008, 32(3): 508-522. [15] 姚叶青, 俞小鼎, 郝莹, 等.两次强龙卷过程的环境背景场和多普勒雷达资料的对比分析[J].热带气象学报, 2007, 23(5): 483-490. [16] 吴俞, 薛谌彬, 郝丽清, 等.强台风"山神"外围超级单体引发的龙卷分析[J].热带气象学报, 2015, 31(2): 213-222.