Vertical Observation Study of Summer Rainfall in Beijing Based on Wind Profiler Radar

Wind profiler radar data was used to retrieve cloud dynamic characteristics, including vertical velocity, droplet terminal velocity, and microphysical parameters such as cloud and rain water mixing ratios. Summer precipitation in Haidian District of Beijing on 7–8 May 2020, was observed and analyzed by retrieval results using weather radar, sounding, automated meteorological readings, disdrometer, and microwave radiometer. Results indicated that the vertically scanning instruments and retrieval results obtained precipitation dynamic and microphysical information that can be used for further studies. The station was near the edge of the main precipitation reflectivity factor and had stratiform cloud precipitation. The overall precipitation reflectivity factor was weak (mainly at 0–20 dBZ), with the vertical shear of horizontal wind at 4 km running through total precipitation. The precipitation was divided into two stages. The earlier stage 2000 BJT (Beijing time) 7 to 0200 BJT 8 May 2020 had shallow convective structures at a lower height, and the convective precipitation cloud top was relatively high (average height 8207 m). Horizontal wind shear at low-level aided the development of convection, and the proportion of 10–20 dBZ was large. The particle spectrum was narrow, with a diameter ＜1 mm, and the rain rate was weak. However, the number concentration was large, reaching a maximum of 26305 m⁻³. Warm advection was present at 2–3 km, water vapor and liquid water values were high, and the rain water mixing ratio range was 0.02–0.15 g/kg. The cloud water mixing ratio range was 0.5–2 g/kg, with a large value and wide distribution. Droplet terminal velocity was 3.2–4.2 m/s, with vertical velocity in the range of ±0.6 m/s, and updraft and downdraft alternated. The later stage (0200–1000 BJT 8 May 2020) became typical stratiform cloud precipitation, with a relatively low cloud top (average height 7831 m). The proportion of ＜10 dBZ was large, the strong value center of the bright band was formed at 3100 m, the particle spectrum broadened, and the maximum diameter was close to 1.5 mm. However, the number concentration decreased, with a maximum value ＜3000 m⁻³. The rain and cloud water values were one order of magnitude lower than that of the convective stage. The intensity range was narrow, the droplet terminal velocity was reduced to 2.8–3.6 m/s, and the vertical velocity was reduced by an order of magnitude compared to the convective stage. There was obvious horizontal orientation upward and downward areas below the height of the bright band (2.5–2.8 km).