Application of Three-Dimensional Wind Fields and Dual-Polarization Signals of an X-band Phased Array Weather Radar in Diagnosing Vertical Motion and Cloud Electrification in Convective Storms

The Hong Kong Observatory (HKO) installed an X-band dual-polarization Phased Array Weather Radar (PAWR) at its wind profiler station at Sha Lo Wan (SLW) in 2021 to monitor high-impact weather in Hong Kong. The PAWR could complete a volume scan in one minute with a spatial resolution of 30 meters. Dual polarimetric variables from the SLW PAWR, including differential reflectivity (Z_DR), specific differential phase (K_DP), and hydro-classification (HCL) products, were used to diagnose the vertical motion and lightning characteristics of mesoscale convective storms (MCS). Through variational data assimilation, three-dimensional (3-D) wind fields were constructed to validate the SLW PAWR observations. Two MCS events that occurred on 18 September 2022 and 17 June 2023 are central to this study. The findings include (1) negative Z_DR serves as a good indicator of the occurrence of intense downdrafts associated with an MCS, a premise further supported by the 3-D wind field analysis results, (2) negative K_DP suggested the formation of vertically aligned ice crystals which facilitated cloud electrification, and (3) HCL products indicated the presence of mixed ice crystals and graupel above the 0°C melting layer which promoted active cloud-to-cloud and cloud-to-ground lightning strokes. These results show that the SLW PAWR provides essential observations, which, when coupled with 3-D wind field analysis, can aid in enhancing the understanding of the dynamics and electrification processes within an MCS.