青藏高原那曲地区地闪与雷达参量关系

基于2014—2015年5—9月西藏那曲地区多普勒天气雷达数据,结合地闪观测数据,识别雷暴单体样本,统计分析了地闪位置附近的雷达回波分布特征,并研究了高原雷暴的雷达参量与地闪频次的相关关系。结果表明:那曲地区地闪发生位置附近的雷达最大反射率因子呈正态分布,峰值分布区间集中于34~41 dBZ。发生地闪位置附近的20 dBZ回波顶主要集中于11~15 km高度,30 dBZ回波顶高分布的峰值区间则为8.5~12 km。分析表明:表征局地雷暴对流发展强度的雷达参量与地闪频次之间一对一的相关关系较差,但相关性随地闪频次增加而增强。基于雷达参量分段统计得到的对应分段平均地闪频次与雷达参量之间表现出较强相关关系,体现了宏观上闪电活动强度与雷暴发展强度之间的正向关系。其中,基于原始数值进行区间划分的强回波（组合反射率因子不小于30 dBZ）面积与平均地闪频次的线性相关系数达0.75,基于对数数值区间划分的7~11 km累积可降冰含量的对数值和地闪频次的线性相关系数达0.95。文中对比了多个雷达参量和地闪频次线性拟合与幂函数拟合结果,整体上幂函数拟合略好于线性拟合。

Relationships Between Cloud-to-ground Lightning and Radar Parameters at Naqu of the Qinghai-Tibet Plateau

Lightning observation may play a key role in the monitoring of deep convection over the Qinghai-Tibet Plateau, especially considering that the wide-range and real-time observation ability of lightning location system. It is firstly necessary to understand the relationship between lightning activity and deep convection features, which, has been rarely concerned in the Qinghai-Tibet Plateau. Using radar data and cloud-to-ground (CG) lightning data during May-September from 2014 to 2015, correlations between CG lightning and radar parameters of thunderstorms are investigated over Naqu, a county in the middle of the Plateau with relatively strong lightning activity. Continuous spatial regions of radar composite reflectivity above 20 dBZ are identified as storm cells at each 6 min radar volume scan, and "matching ellipses" are used to enclose the scope of cells, and then whether CG lightning flashes fall in ellipses or cells is decided. Cells with lightning and located within 30-100 km of radar center are picked out as thunderstorms. Based on 5626 thunderstorm samples, it is summarized that the maximum radar echo, 20 dBZ echo top and 30 dBZ within 5 km of CG flash location exhibit normal distribution, with their peak values ranging from 34 to 41 dBZ, 11 to 15 km, and 8.5 to 12 km, respectively. Meanwhile, the maximum vertical integrated liquid content and the maximum precipitation ice content vertically integrated at 7-11 km both show logarithmic normal distribution. A total of 4719 thunderstorms that possess no less than 30 dBZ reflectivity (a threshold value for the definition of strong reflectivity) are selected for the correlation analysis. Weak correlations between CG lightning frequency and radar parameters are found while are considered as one-to-one relationships. However, correlations enhance prominently when the CG lightning frequency in the thunderstorm increases. The correlation study based on interval segmentations of radar parameters is then made and strong relationships are found, indicating the macroscopic correspondences of CG lightning frequency to the intensity of thunderstorms. The area of composite reflectivity no less than 30 dBZ show the most outstanding correlation with CG lightning frequency among radar parameters which are segmented linearly, with the correlation coefficient being 0.75. Among radar parameters that are segmented according to their logarithms, the logarithm of precipitation ice content accumulated at 7-11 km and in the area with composite reflectivity no less than 30 dBZ are most prominently correlated with CG lightning frequency, with the correlation coefficient being 0.95. Formulas based on linear fittings and power function fittings are all given, while the power function fittings are a little better according to their corresponding correlation coefficient.