Characteristics of summer rainfall droplet spectra in mountainous and non-mountainous areas of the Jianghuai region

Analysis of raindrop spectrum characteristics is an important method to study the microphysical characteristics of precipitation. In this paper, raindrop spectrum data collected at four stations in Anhui province from June to August of 2011—2012 are used to investigate raindrop spectra of convective precipitation and stratiform precipitation in mountainous and non-mountainous areas and compare their similarities and differences. The precipitation is divided into convective precipitation and stratiform precipitation according to the rainfall rate and its variation with time. The main conclusions are as follows. The mountain terrain has a greater impact on the raindrop spectrum of convective precipitation, but a smaller impact on the raindrop spectrum of stratiform precipitation. When the rainfall intensity is the same, the concentration of raindrops in convective precipitation in mountainous areas is larger than that in non-mountainous areas, while the size of raindrops is smaller than that in non-mountainous areas. The raindrop number concentration and raindrop size of convective precipitation in mountainous and non-mountainous areas both increase with rainfall intensity. The relationship between N_w (standardization parameter) and raindrop number concentration is studied. It is found that N_w is related to raindrop number concentration, but it cannot fully reflect the change of raindrop number concentration, and is not sensitive to the change of rain intensity. When the rainfall intensity is the same, the difference in raindrop number concentration between mountainous and non-mountainous convective precipitation is small, yet the difference in N_w is obvious, which indicates that N_w can better reflect the difference of precipitation mechanism between mountainous and non-mountainous areas. For weak convective precipitation with rainfall intensity less than 30 mm/h, the concentration of small raindrops in mountainous areas is relatively close to that in non-mountainous areas, while the concentration of large raindrops is lower than that in non-mountainous areas, which corresponds to a narrower spectral width of raindrops, indicating that terrain impact on raindrop spectra is more obvious. For strong convective precipitation with rainfall intensity greater than 30 mm/h, the rainfall droplet spectra in mountainous and non-mountainous areas are relatively close, which indicates that terrain impact on the rainfall droplet spectra is significantly weakened. Precipitation type have little influence on the Z (radar reflectivity)-R (rainfall rate) relationship in mountainous area.