Vertical Distributions of Raindrops and Z-R Relationships Using Microrain Radar and 2-D-Video Distrometer Measurements During the Integrative Monsoon Frontal Rainfall Experiment (IMFRE)

The vertical characteristics of raindrop size distributions (DSD) and Z-R relationships for monsoon frontal rainfall have been investigated using the co-located two-dimensional video disdrometer and micro rain radar at the Xianning surface site, and the S-band weather radar at the Wuhan radar site during the Integrative Monsoon Frontal Rainfall Experiment (IMFRE). In this study, a total of 1,896 rain samples (1-min resolution) were collected and classified into three categories of convective rain (CR), stratiform rain (SR), and light rain (LR), and their corresponding rain microphysical properties were explored. The LR category is dominated by the evaporation of smaller raindrops and the break-up processes of larger raindrops, resulting in decreasing trends in radar reflectivity and rain rate as the raindrops fall. The SR category undergoes a competition of break-up and coalescence processes, with weak increases in radar reflectivity and rain rate. Whereas, for the CR category, the coalescence process is dominant on the falling path of raindrops, especially below 1 km, leading to sharp increases in radar reflectivity and rain rate. The microrain radar data at height of 200 m is quantitatively compared with the two-dimensional video disdrometer data, and a good agreement is found between them. Further, the number concentrations of raindrops are negatively correlated with the diameters of raindrops and discrepant significantly at different heights among the three rain categories. The height-dependent Z-R relationships found for LR, SR, and CR categories will provide insightful information for improving radar rainfall estimate of monsoon frontal rainfall over central China in the future.