Characteristics of Raindrop Size Distribution in Chengdu

Based on raindrop data derived from LNM laser spectrometer from 2009 to 2011, raindrop size distribution (RSD) characteristics of Chengdu are discussed, and evolutions of microphysical parameters of 175 precipitation processes including cumulus type, cumulus-stratus mixed cloud type and stratus type are analyzed. Meanwhile, three typical cases are chosen to investigate the microphysical structure parameters. Conclusions are as follows.The cumulus precipitation and cumulus-stratus mixed cloud precipitation are wider than stratus precipitation in RSD and larger than stratus precipitation in raindrop density, especially in sections of big raindrops and very small raindrops. It reveals different ways raindrop growth. The curve of RSD in three types of precipitation has more than two peaks, indicating that most of the precipitation process is unstable. The advantage diameter and the median volume diameter are well correlated with rainfall intensity, D_p and D_n values in three types of precipitation are significantly different, the advantage diameter and the median volume diameter of stratus precipitation is less than half of cumulus precipitation. In general, four kinds of characteristic diameters of the cumulus precipitation are the largest ones in three types of precipitation, and the ones of the cumulus-stratus mixed cloud precipitation are larger than those of the stratus precipitation. But results are not completely in accordance with facts. Because of the complexity of the precipitation process, four characteristics of diameter cannot be the classification standard of precipitation patterns. Small raindrops make the main contribution to the rainfall intensity of stratus precipitation, while big raindrops make the main contribution to the cumulus precipitation and cumulus-stratus mixed cloud precipitation over Chengdu Area. In different rainfall process, raindrop is in the majority, the deviation of contribution rate is small, and the number proportion is stable. Although the number of big raindrops is very small, the deviation of raindrop density ratio becomes large and the proportion of number is not stable, and it is the main cause for heavy rainfall process. The rainfall intensity depends on the quantity of big raindrops, however, the contribution of small raindrops to the rainfall intensity is negative. The median volume diameter can indicate the change of rainfall intensity, because the median volume diameter always increases earlier than rainfall intensity. Raindrop proportion increases firstly, then the raindrop density increases, finally, numbers of the small raindrops increase with big raindrops, strengthening the rainfall intensity. The study on RSD is helpful to further understand the mechanism and microphysical characteristics of the precipitation over Chengdu, and can also accumulate basic data and experience for the precipitation numerical prediction.