Analysis of the polarimetric characteristics of hail storm from S band dual polarization radar observations

This study aims to investigate the polarimetric radar characteristics of hail storm and application of these characteristics for operational work. A total of 46 hail storm reports that have been observed with the S-band dual-polarization radar are used for this study. Three polarimetric signatures, i.e., the polarimetric variables of hail at various height, Z_dr column, the polarimetric TBSS, are repeatedly found in these hail storms and analyzed with the focus on the differences between polarimetric signatures of large and small hails. The study yields the following results: (1) The median value of Z_h for large hails is higher than the value for small hails. A significant overlap of the Z_h distributions for large and small hails is also present. (2) The variation of polarimetric variables of hail is concentrated below the melting level. Compared with small hails, large hails have lower Z_dr and correlation coefficient (CC) values. (3) The maximum height of Z_dr column can reach the −10℃ level in all of the hail storms, while 83% of large hail reports and 46% of small hail reports show that the Z_dr column could penetrate the −20℃ level. (4) The evolution of the Z_dr column height is an appropriate index that can reflect the development of the hail storm. During a continuous hail process, the re-development of the Z_dr column height occurs earlier than that of the hail storm. It is also found that the peak of Z_dr column height usually occurs about 24 min (median value) prior to a large hail report and about 11 min (median value) prior to a small hail report. (5) The polarimetric TBSS is a good indicator for identifying hails aloft, especially when there are other precipitation echoes located radially behind the hail core. In this study, the polarimetric TBSS can be found in all of the large hail reports and in 52% of the small hail reports.