中国龙卷时空分布及其环境物理量特征

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。 

THE SPATIAL AND TEMPORAL DISTRIBUTION OF CHINESE TORNADOS AND THEIR CHARACTERISTICS ANALYSIS OF ENVIRONMENTAL PHYSICAL VARIATIONS

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.