Vertical microphysical structures of summer heavy rainfall in the Yangtze-Huaihe River Valley from GPM DPR data

Abstract

Increasing heavy rainfall poses significant challenges in the Yangtze-Huaihe River Valley (YHRV). There is a need for more specific insights into the vertical microphysical structures and their influence on heavy rainfall to enhance the accuracy of numerical simulations and forecasts. Using data from the Dual-frequency Precipitation Radar (DPR) on the Global Precipitation Measurement (GPM) satellite from 2014 to 2023, this study investigated the vertical microphysical structures of different types of heavy summer rainfall (> 8 mm/h) and elucidated their impacts on the rain rate in the YHRV. Based on the radar reflectivity thresholds at different altitudes, heavy summer rainfall was classified into four types: deep convective, shallow convective, stratiform rainfall, and warm rainfall. In the YHRV region, shallow convective rainfall contributed the most to total heavy rainfall (39.1 %) and had the highest occurrence (44.7 %) of extreme rainfall (>50 mm/h). Stratiform rainfall occurred most frequently but decreased rapidly with increasing rain rates, while warm rainfall contributed little to heavy rainfall. For the vertical microphysical structure of heavy rainfall, deep convective rainfall exhibited rapid growth of large particles above the melting layer, resulting in the largest average mass-weighted diameter (Dm) near the surface (2.2 mm), but the smallest average droplet concentration (recorded as dBNw in the decibel scale), approximately 37. Below the melting layer, the Dm of small particles in the shallow convective rainfall increased rapidly, and the impact of coalescence was much greater than that of break-up. Except for warm rainfall, the average Dm for other types of heavy rainfall remained relatively high, exceeding 1.5 mm both within and below the melting layer. The average dBNw increased consistently as altitude decreased. As rainfall intensified to extreme rainfall, the average rain rate of shallow convective rainfall slightly surpassed that of deep convective rainfall. This was due to a decrease in average dBNw for deep convective rainfall, while the average dBNw of shallow convective rainfall continued to increase.