山西云微物理特征的地面观测

利用连续气流纵向热梯度云凝结核仪和激光降水粒子谱测量仪对山西地面的云凝结核和雨滴谱进行了观测研究.研究结果表明,云凝结核(CCN)数浓度具有明显的日变化特征,1天出现了两次峰值,数浓度日变化与气象因子、人类活动有关.降水对CCN具有冲刷作用.利用关系式NCCN=CSk拟合得到的地面CCN活化谱参数C值明显较大,k值较高,属于典型的大陆型核谱.对层状云、层积云降水雨滴微物理特征参量分析发现:3次层状云、层积云降水雨滴数密度变化范围分别为74～229 m-3、305～743 m-3,平均含水量量级分别为10-2 g/m3、10-1g/m3,最大雨滴直径分别为1.78 mm、4.7 mm.对层状云降水雨滴的数密度和雨强贡献较大的分别是小于1 mm、0.2～2 mm的雨滴;对层积云降水雨滴的数密度和雨强贡献较大的分别是0.2～2 mm、1～3 mm的雨滴.层积云出现稳定谱的比例高于层状云.从瞬时谱型分布看,层状云出现单、双、三峰多,第四、五峰值的频率比较少,层积云雨滴谱分布没有出现指数型,常有多峰.从平均谱分布看,层状云谱宽窄于层积云,层状云雨滴平均谱服从指数分布,层积云曲线呈向下弯曲的趋势.对汾阳2008年7月17日一次积层混合云降水雨滴谱资料分析发现积层混合云降水雨滴微物理量起伏大,降水雨强主要由雨滴数密度决定.相同雨强下,若有相对更多的大雨滴,雷达反射率会更大一些.随着强回波云块的过境,雨滴数浓度、雨滴谱峰值个数、谱宽均明显增大.

Ground Observation of Microphysical Properties in Shanxi Province

Using a DMT(Droplet Measurement Technologies) continuous flow streamwise thermal gradient cloud condensation nuclei(CCN) counter and the precipitation particle spectrometer, ground measurements of CCN and raindrop size distribution in Shanxi were conducted. According to the observation, affected by meteorological factors and human activities, the CCN concentration variations had a distinctive diurnal cycle with two apparent peaks. Precipitation had an scavenging effect on CCN particles. According to the expression N_CCN=CS^k, the CCN spectra can be derived. The fitting spectra parameters C (more than 2000) and k (less than 1) show the continental characteristic of CCN in Taiyuan. Microstructure parameters for stratiform and stratocumulus cloud precipitation were analyzed. It was found that the number concentrations of raindrop were 74-229 m^-3 and 305-743 m^-3, the average of liquid water magnitudes were 10^-2 g/m³ and 10^-1 g/m³ and the maximum raindrop diameters were 1.78 mm and 4.7 mm of three stratiform and stratocumulus cloud precipitation, respectively. Less than 1 mm and 0.2-2 mm raindrops made a bigger contribution to the number concentration and rainfall intensity of stratiform cloud precipitation. 0.2-2 mm and 1-3 mm raindrops made a bigger contribution to the number concentration and rainfall intensity of stratocumulus cloud precipitation. Stable spectra appeared in stratiform cloud were more than that of stratocumulus cloud. From the instantaneous spectrum distribution, most of stratiform raindrop size distribution had single, double, and three peaks and less stratiform raindrop size distribution had four and five peaks. Stratocumulus raindrop size distribution exhibited the multi-peak distribution mainly and no exponential distribution. From the average spectrum distribution, spectral width of stratiform cloud was narrower than that of stratocumulus cloud. Stratiform raindrop size distribution showed the exponential distribution. Stratocumulus raindrop size distribution displayed downward trend. The characteristics of raindrop spectra of convective-stratiform mixed cloud precipitation in Fenyang on 17 July 2008 were analyzed. The fluctuation of microphysical parameters was strong. The rainfall intensity was largely determined by the number concentration of raindrops. Under the same rainfall intensity, if there were more big size raindrops, radar reflectivity was even more. Through the strong echo, the number concentration, number of peaks, and spectral width were increased.