基于地面雨滴谱资料分析层状云和对流云降水的特征

根据由声雨滴谱仪器测量得到的雨滴谱资料,结合降水云的结构来将降水云系划分成为对流云降水云系和层状云降水云系.分析这两种降水云系中的稳定雨滴谱特征,包括雨滴谱的各种特征直径(平均直径Dm、众数直径Dd、平均体积直径Dv、优势直径Dp、中数直径Dna和中数体积直径Dn)、峰值结构和Z-R关系等.通过对这些量的分析,进一步分析划分降水云系的判据.

Characteristics of Rain from Stratiform Versus Convective Cloud Based on the Surface Raindrop Data

It is very meaningful to separate the precipitation cloud system into convective cloud and stratiform cloud.The separation is important to improve the remote sensing of precipitation and compute the heat momentum,and so on.The raindrop size distribution and the structure of precipitation cloud are used to separate the precipitation cloud system into convective cloud and stratiform cloud.In Beijing,the time of convective precipitation is short.Some convective precipitation lasts just half an hour.Moreover,during the precipitation,there often exists lightning and thunder.The time of stratiform precipitation,which lasts at least 5 hours,is longer than that of convective precipitation.The bottom of stratiform cloud is low and has mean structure.First of all,the equilibrium raindrop size distributions are analyzed.The equilibrium raindrop size distributions are continuous and have the similar characteristics in the width of the spectra and maximum of N(D),and so on.Six kinds of diameters are calculated,including the mean diameter D_(m),the mode diameter D_(d),the mean volume diameter D_(v),the predominant diameter D_(p),the median volume diameter D_(n) and the median diameter D_(nd).It is found that for convective cloud D_(v)>1.20 mm,and D_(n) >1.5 mm.The peak of raindrop size distribution is analyzed.There is no single peak of raindrop size distribution in the convective precipitation,however,there exists in stratiform precipitation.The raindrop size distributions are separated into 3 kinds,such as single-peak raindrop size distribution,double-peak raindrop size distribution and three-peak raindrop size distribution.The diameters corresponding to the peaks are analyzed.The rain-rate R and the radar reflectivity factor Z are calculated using the equilibrium raindrop size distribution,and then the relationship between R and Z are calculated.Compared with the stratiform cloud precipitation,the factor of the relationship is high for convective cloud precipitation.The factor is lager than 200 for convective cloud precipitation,and the factor is smaller than 200 for stratiform cloud precipitation.All the informations can be used to separate precipitation cloud into convective cloud and stratiform cloud.But the precipitation is complex,so it should be careful to use one of the informations.