Characteristics of Raindrop Size Distribution in a Mei-Yu Front Heavy Rainfall Process over Central China

Characteristics of raindrop size distribution (DSD) in a heavy rainfall process during the Meiyu season has been investigated using the surface measurements from 11 Particle Size and Velocity (PARSIVEL) disdrometers in Hubei Province, central China. Based on this case study, we draw the following conclusions. (1) The contribution of raindrops with different diameter (D) from different sites to precipitation is similar to each other. For example, the contributions of raindrops with D < 1 mm, 1 mm < D < 2 mm and D > 2 mm to the total precipitation are 10%, 50% and 40%, respectively, when the daily accumulated precipitation fall between 50 and 70 mm. However, it can be up to 50% for D> 2 mm when the daily precipitation exceeds 100 mm. Also, the distribution of number concentration of raindrops with different size at each site is similar. The ratios of the number concentrations of raindrops with D < 1mm, 1 mm < D < 2 mm and D > 2mm to the total number of raindrops are between 50%−60%, 30%−40% and less than 10%, respectively. (2) The fitted power-law relationships between the generalized intercept parameter (Nw) and mass-weighted mean diameter of raindrops (Dm) strongly depend on Dm, but it is not true for the relationships between Dm and rain rate (R). (3) The shape-slope relationship of the gamma distribution and the radar reflectivity (Z)–R relationship (Z=aR^b) is derived based on the observations where the exponent b varies from 1.26 to 1.44, while the coefficient a varies in a large range. These results differ to the results over the ARM SGP site (Wang et al. 2016) in relationships between Z and R, the Gamma shape μ and slope λ parameters, the intercept parameters and λ. The focus of this study is on the raindrops with D ≤ 6 mm in a heavy rainfall process. However, the research of Wang et al was focused on raindrops with 0.12 mm ≤ D ≤ 4 mm in the stratiform rain regions of Deep Convective Systems.

Key words:Raindrop size distribution; Meiyu; Heavy rainfall process; Central China