安徽滁州夏季一次飑线过程的雨滴谱特征

Characteristics of Raindrop Size Distribution for a Squall Line at Chuzhou of Anhui During Summer

选取2014年7月31日安徽滁州一次飑线过程,使用地基雨滴谱仪资料分析此次过程的雨滴谱特征。根据雷达回波和地面降水强度将这次降水过程划分为对流降水、过渡性降水和层云降水,并以10 mm·h^(-1)为临界值将对流降水进一步划分为对流前沿降水、对流中心降水、对流后沿降水。结果表明:对流中心降水、过渡性降水、层云降水的质量加权直径均比较稳定,平均值分别为1.8 mm,1.0 mm,1.7 mm。对流降水的标准化截距相比层云降水更大。对流中心降水各粒径段雨滴数浓度均较高;层云降水小雨滴浓度较低,且有少量大雨滴;过渡性降水由小雨滴组成。当雨水含量相同时,层云降水的质量加权直径相比对流降水更大。当雨强相同时,层云降水的反射率因子相比对流中心降水更大。更为精细的降水类型划分可有效改善Z-I关系。

Characteristics of raindrop size distribution are analyzed using a ground-based disdrometer for a midlatitude squall line at Chuzhou of Anhui on 31 Jul 2014.The observational precipitation are classified into convective rain,transition rain and stratiform rain based on the radar reflectivity and rain rate at surface.The convective rain is divided into leading edge,convective center and trailing edge according to a threshold rain rate 10 mm · h^(-1).The raindrop spectrum characteristics in different precipitation regions are studied.Results show that the mass-weighted diameter for convective center,transition region,stratiform region are stable with mean values of 1.8 mm,1.0 mm and 1.7 mm,respectively.The generalized intercepting parameter N_W of convective precipitation is larger compared with stratiform precipitation,indicating a larger number concentration of drops.The μ value is the largest for transition precipitation but the smallest for convective precipitation.The raindrop spectrums are different for varied rain type.For convective precipitation,it shows a highest concentration of raindrop within each size range,especially for small size of raindrops,which results in a smaller raindrop size than tropic region.For stratiform precipitation consists of a lower number concentration of small drops and less large raindrops,therefore,the spectrum curve is flat.For transition precipitation,the number concentration of small drops is close to stratiform precipitation without large drops,results in a steep spectrum.The mass-weighted diameter for leading edge is large probably caused by gravity separation at the early stage of precipitation.The rainwater content of stratiform precipitation is smaller compared with convective precipitation.The mass-weighted diameter of stratiform precipitation is larger compared with convective precipitation,and it increases more rapidly compared with convective precipitation as the rain water content increasing.The reflectivity is larger for stratiform precipitation compared with convective center precipitation at the same rain rate.The ZJ relationship of stratiform precipitation is Z=409I^(1.48) when partitioning the rain into convective rain,transition rain and stratiform rain,but Z=395I^(1.51) when the partitioning is blurred.The Z-I relationship is improved and the accuracy of radar rainfall estimates is enhanced by dividing the rain type more exactly.In summary,although the raindrop size distribution for a squall line at ground is discussed,the knowledge on microphysical process of mid-latitude squall line is still insufficient.Dual polarization radar can be applied to further investigate the microphysical process in different types of internal cloud precipitation in the future.