Microphysical characteristics of extreme convective precipitation over the Yangtze-Huaihe river basin during the Meiyu season based on polarimetric radar data

The S-band polarimetric radar data and hourly rain gauge data during the Meiyu seasons of 2013 and 2014 were used to examine the microphysical characteristics of extreme convective precipitation over the Yangtze-Huaihe river basin. Two types of extreme convective precipitation features (PFs) are identified based on the top 1% rainfall rate (top-R) and the top 1% 20 dBz echo top height (top-H). Result shows that only ~30% of the samples are overlapped between these two types of PFs, which indicates a weak linkage between them. Microphysical differences between the top-R (characterized by R>46.2 mm/h in this study) and the top-H (H>14.5 km) are further analyzed. For the same Z_H near the ground, Z_DR values in top-R are always ~0.2 dB lower than that in top-H, indicating the former contains relatively smaller size. Combination of the drop size distribution (DSD) retrieval and hydrometeor classification results shows that both types of precipitation systems possess characteristics of maritime convection. However, top-R (top-H) PFs contain smaller (larger) raindrops with higher (lower) number concentration of raindrops, resulting in more (less) intense rainfall. On the other hand, the reflectivity of top-H PFs reaches higher altitude with stronger vertical velocity, resulting in more water vapor and super-cooled liquid water being transported aloft. Ice particles can grow larger (e.g., graupel and hail) and then melt into larger raindrops. This study shows that there is a weak correlation between the rainfall intensity and the depth of convection while the extreme rainfall is usually accompanied by moderate convection during the Meiyu season.