Dual polarization characteristics of an elevated thunderstorm hail event in the Nanling region

An elevated thunderstorm hail event occurred in Chenzhou and its vicinity in the Nanling region during March 22-23, 2023. A wide range of hail with diameters reaching up to 20 mm was reported, which was rare in elevated convection. In order to enhance the capability of forecasting and early warning of such hail events, this paper uses conventional meteorological observation data and SA-band dual-polarization radar products to analyze its weather conditions and dual-polarization radar echo characteristics. The results are as follows. (1) This event occurred in the cold area on the north side of the surface front, which was a typical elevated thunderstorm process. The hail-falling area was located 140 km to the north side of the surface front, and the large hail of 20 mm in diameter was caused by a supercell storm. (2) The storms that caused large hail in southern Chenzhou can be divided into four stages, which are the initial stage, the rapid development stage, the hail-falling stage, and the weakening stage. During the rapid development stage, the strong echo center increases rapidly and the vertical cumulative liquid water content (VIL) increases sharply. The differential reflectivity (Z_DR) column extends to 4~5km above the 0 ℃ layer. A stronger updraft provides favorable conditions for hail development. During the hail-falling stage, with the rapid decrease of the strong echo center, the weak echo region (WER) disappears, and the height of the Z_DR column decreases significantly. The values of Z_DR and specific differential phase (K_DP) gradually increase as the melting hail falls toward the ground. While the footprints of K_DP correspond well with the hail-falling region. (3) The three-body scattering (TBSS) characteristics of large hail showed that the Z_DR value at the root was large, which then decreased rapidly with the increase of radial distance, and the cross-correlation coefficient (CC) was significantly low. The sidelobal echo features of large hail indicate a low Z_DR and low CC signature. These dual polarization features are key concerns for the large hail warning.