Investigation of raindrop size distribution and its potential influential factors during warm season over China

The nation-wide feature of raindrop size distribution (hereafter referred to as DSD) remains largely unknown across China. We here analyzed the DSD using high-resolution disdrometer measurements collected throughout China during the warm season (May through August) of 2020. Overall, pronounced unimodal structures were found for the monthly mean DSD, while little differences were revealed in the monthly variation of DSD. Spatially, the regions with a high value of mass-weighted mean diameter Dm generally witnessed a low value of intercept parameter Nw. The DSD parameters were further investigated by six regions of interest: Northeast China Plain (ECP), North China Plain (NCP), Yangtze River Delta (YRD), Pearl River Delta (PRD), Sichuan Basin (SCB), and Qinghai-Tibet Plateau (QTP). Specially, Dm (log10Nw) over ECP, NCP, YRD, PRD and SCB was found to have a larger (smaller) value than the surrounding areas, whereas the Dm (log10Nw) in the QTP had a smaller (larger) value. Furthermore, explicit analyses were performed in attempt to better understand the influential factors accounting for the regional disparity of DSD by two categories: stratiform and convective precipitation. Dm, log10Nw, spectral width and peak concentration all showed larger values in the convective precipitation than those in the stratiform precipitation. Interestingly, the Dm-log10Nw pairs for convective precipitation resembled roughly the “maritime” cluster, indicating a maritime nature of convective precipitation throughout the warm season in China. The PRD had the largest Dm and the smallest log10Nw, while the QTP had the smallest Dm and the largest log10Nw in the stratiform precipitation. In addition, several widely used empirical equations of Z-R relations tended to underestimate R compared with our actual fitting. The impacts of environmental variables were further studied, including convection available potential energy (CAPE), surface temperature, wind shear and vertically integrated moisture flux divergence (MFD). The dependence of DSD on environmental variable was revealed to varying degrees. It is noteworthy that larger CAPE but lower MFD was found to be accompanied with heavy rain produced by convective precipitation than by stratiform precipitation. The invaluable DSD dataset hereby will lay a solid foundation for potentially improved quantitative precipitation estimation from weather radar in the future in China.