不同尺寸冰雹S波段双偏振雷达偏振量特征统计

冰雹大小影响天气灾害的程度，为发展基于双偏振参量识别冰雹大小的算法，筛选了2019年、2020年山东省发生的33例冰雹事件，依据我国冰雹等级划分标准将其划分为小冰雹、大冰雹、特大冰雹，基于湿球0 ℃及冰雹融化特性确定了7个高度层，探讨了3类冰雹在不同高度层的双偏振参量分布特征，并获得了冰雹的偏振参量阈值。研究表明:在相同高度，冰雹越大雷达水平反射率因子Z_h中位数越大、差分反射率因子Z_dr中位数越小且基本为正值，但在-10~-20 ℃层，大冰雹的Z_dr中位数易呈现负值；相关系数CC中位数随冰雹增大或高度降低而减小，但特大冰雹在0 ℃层到H_{0 ℃}-1 km (0 ℃层下1 km) 之间由于融化比例较小CC反而会稍大；冰雹差分相移率K_DP中位数在0 ℃层以上为0 °/km左右，在0 ℃层以下随高度降低冰雹融化而增加；大冰雹或特大冰雹基本特征是Z_h大、CC小、Z_dr小，CC可低至0.7以下，所有冰雹的Z_dr、K_DP可出现负值，小冰雹Z_dr大于0 dB的情况较多，特大冰雹Z_dr接近0 dB；-20 ℃层以上的Z_h、0~-20 ℃层的CC和Z_h、0 ℃层以下的CC、Z_h、Z_dr对冰雹大小比较敏感。 

STATISTICAL ANALYSIS OF POLARIMETRIC CHARACTERISTICS OF DIFFERENT SIZE HAILS FOR S-BAND DUAL POLARIZATION RADAR

Hail size affects the degree of weather disasters. Aiming at developing an algorithm for hail size discrimination based on dual polarization parameters, the present study selected 33 hail events occurred in 2019 and 2020 in Shandong Province, and categorized them into small, large, and giant hails according to the Hail Classification Standard in China. Then seven altitude levels were determined based on the wet bulb 0 ℃ level and the properties of melting hails, the distribution characteristics of dual polarization variables of three types of hails at different altitude levels were discussed, and the thresholds of the polarization parameters for hails were obtained. The results show that the larger the hails are, the larger the median Z_h and the smaller the median Z_dr are at the same altitude, but the median Z_dr are more likely to be negative in the -10~-20 ℃ layer. While the median CC basically decreases with the increase of hails or decrease of height, that of giant hails are slightly larger than the large hails in the 1 km below the 0 ℃ layer due to smaller melting ratio. The medians for K_DP of hails are about 0 °/km above the 0 ℃ layer, and they increase with hail melting as height decreases below the 0 ℃ layer. Moreover, the basic characteristics of large or giant hails are large Z_h, small CC less than 0.7 and small Z_dr. Z_dr and K_DP can be negative for all hails, but Z_dr is more likely to be more than 0 dB for small hails and close to 0 dB for giant hails. Finally, the more sensitive polarization parameters to hail size at different altitude layers include Z_h above the -20 ℃ level, CC and Z_h in the 0~-20 ℃ level, and CC, Z_h and Z_dr below the 0 ℃ level.