Abstract:
Herein, using a high-resolution simulation produced by the weather research and forecasting model, along with a three-dimensional precipitation equation and the concept of precipitation efficiency, a heavy rainfall event that occurred in Mianning on June 26, 2020, is studied. The vertical dynamic structure, hydrometeor distribution, and various physical processes involved in precipitation are compared and analyzed. The characteristics related to water substances (i.e., water vapor, rain, snow, hail, graupel, ice, and liquid cloud) in complex terrain areas are further revealed. Results indicate that the rainstorm process can be divided into two stages. In the first stage, spanning from 1800 BJT to 2200 BJT (Beijing time) on June 26, 2020, the intense uplift within the strong precipitation area promotes the convergence of water vapor and liquid-phase hydrometeors from the weak precipitation area. The abundant liquid-phase hydrometeors collected in the strong precipitation area convert into heavy rainfall and ice-phase hydrometeors to induce cloud growth. At this time, a strong convective echo exhibiting a reflectivity of >35 dB
Z reaches the maximum height. In the second stage, spanning from 2300 BJT 26 to 0100 BJT 27 June 2020, the uplift in the strong precipitation area weakens, leading to a reduction in the convergence of liquid-phase hydrometeors, but. However, the convergence of water vapor remains strong, and the location of maximum ascending motion descended, which facilitates the condensation of water vapor as well as the collision between clouds and raindrops. Two maximum centers of ascending motion are observed in the vertical direction. The echo intensity displays a strong–weak–strong pattern. Ice particles in the upper atmosphere likely serve as seeds for lower clouds, aiding the conversion of liquid-phase hydrometeors into heavy rainfall. Furthermore, the precipitation efficiency varies considerably across different rainfall intensity ranges, from 5% to 70%; the greater the precipitation efficiency, the stronger the surface precipitation.