Characteristics of Raindrop Size Distribution at Anxi of Fujian

Abstract

Observation of raindrop size distribution (DSD) is significant for the understanding of precipitation physical processes and improvement of radar quantitative rainfall estimation. Based on DSD measurements from 2017 to 2020 collected in Anxi, Fujian Province, the DSD variation characteristics in different seasons and different rain types are analyzed. Subsequently, local empirical relation between radar reflectivity Z and rain rate R and that between Gamma shape parameter μ and slope parameter Λ are proposed. The DSDs observed in the local area are compared with counterparts obtained in other typical areas of China. The results show that DSDs in Anxi exhibit apparent seasonal variation. Generally, raindrops in summer can be the largest with the highest number concentration, while raindrops are the smallest in winter and the number concentration in spring is the lowest. With the increase of particle size, the seasonal variation of the number concentration of raindrops is similar to that in Taoyuan, Taiwan Province, China, while the number concentration of small raindrops is different. Compared with East China and North China, DSDs for summer stratiform precipitation in Anxi have higher concentration of small raindrops, while the concentrations of medium to large raindrops are similar to those in East China. For convective precipitation, the DSDs concentration is similar to that in North China for small raindrops while similar number concentration of medium raindrops to that in East China, while the number concentration of large raindrops is between that obtained in East China and North China. The Z-R relationship of summer stratiform precipitation is in good correspondence with the results obtained in Taoyuan. With the same Z, the R in East China is slightly larger than that in Anxi and Taoyuan; the Z-R relationship for convective precipitation in Anxi is also close to that in Taoyuan. When Z is not greater than 40 dBZ, the Z-R relationship in East China is very close to that in Anxi; when Z exceeds 40 dBZ, R in East China is significantly larger than that in Anxi and Taoyuan. When the slope parameter is larger than 2.5 mm-1, the relationship between the shape parameter μ and slope parameter Λ of the summer Gamma spectrum in Anxi is similar to that in Florida.

Keywords

• characteristics of raindrop size distribution
• seasonal variation
• μ -λ relationship