Nowcasting cloud-to-ground lightning over Nanjing area using S-band dual-polarization Doppler radar

Abstract The method of using S-band dual-polarization Doppler radar-derived parameters to nowcast the cloud-to-ground (CG) lightning of summer (June–August) in Nanjing was examined. The radar data, CG lightning location data and upper-air sounding data during the summer of 2014 were examined for the selected cells. Five reflectivity thresholds (25, 30, 35, 40 and 45 dBZ) at three isothermal levels (− 10 °C, − 15 °C, − 20 °C) were analyzed, and 40 dBZ reflectivity at − 10 °C isothermal level was found to be a good predictor. In addition, hydrometeor identification (HID) based on the dual-polarization parameters was also used to analyze the hydrometeor types in the life cycle of cells, and it was indicated that the presence of graupel and ice crystals at − 10 °C isothermal level was a clear lightning initiation signature. In order to further improve the efficiency and accuracy of nowcasting, the combinations of reflectivity thresholds and HID at certain levels were examined. The compared results showed that the combination of 40 dBZ reflectivity and the identification of graupel at − 10 °C isothermal level was the optimal predictor, with the probability of detection (POD) of 87%, false alarm rate (FAR) of 2%, critical success index (CSI) of 85%, and mean lead time of 13.3 min. The conclusions prove that the proposed optimal predictor is operationally useful and efficient of lightning nowcasting over Nanjing area.