粒子边缘粘连对0℃层亮带雷达反射率因子的影响分析  

Analysis on Contribution of Edge Conglutination between Particles in Cloud to Radar Brightness Band

作　　者：王蒙[1,2] 王振会[1,2] 王云[2] 董慧杰[3] 

机构地区：[1]南京信息工程大学气象灾害预报预警与评估协同创新中心中国气象局气溶胶云降水重点实验室,南京210044 [2]南京信息工程大学大气物理学院,南京210044 [3]南京信息工程大学大气科学学院,南京210044

出　　处：《高原气象》2016年第5期1401-1408,共8页Plateau Meteorology

基　　金：国家自然科学基金项目(41275043);公益性行业(气象)科研专项(GYHY201306078);江苏高校优势学科建设工程资助项目(PAPD)

摘　　要：针对云中粒子在融化、并合过程中的粘连现象对0℃层亮带的影响分析,利用离散偶极子近似算法(DDA)计算融化过程中两个大小相同的球形粒子在雷达发射波偏振方向上发生粘连后的散射特性,以两个等体积融化球为例,它们在雷达发射波偏振方向上发生粘连时的总后向散射截面σDDA,并与同体积融合球的后向散射截面σmieequal比较。结果表明:(1)在等体积直径较小时,σDDA/σmieequal≥1.5,随着等体积直径的变大,σDDA/σmieequal会减小趋向于1,甚至会<1;(2)在同样的等体积直径处,σDDA/σmieequal随着融化程度的加深而增大,在谐振区可出现减小。引入"粘连概率p"参数刻画粘连影响,并应用于含有0℃层亮带的层状云的雷达反射率因子的定量模拟试验。结果表明,在粒子融化、并合过程中,在雷达发射波偏振方向上的粘连,可以有效地增大雷达反射率因子、使亮带现象更加突出。Taking two small, spherical particles for example, the backscattering cross-section as a whole during the stage of edge conglutination between them would be greatest as compared with that before they contact with each other and that after they fuse and coalesce into a single spherical particle, especially the conglutination and coalescence process starts from two small, spherical ice particles. The paper studies the contribution of this phe- nomenon to radar bright band. DDA is used to calculate DDA, the backscattering cross-section of the edge-con- glutinated particles. It has been found that DDA in case the conglutination is along the direction of radar wave po- larization may be 1.5 times greater than mie, the backscattering cross-section of the equal volume, spherical par- ticle at a certain size though the ratio may decrease to even less than 1 and fluctuate as the particle size increases because of resonance for large particles. Introducing ＇ probability of edge conglutination＇ as a parameter to depict the effect of edge conglutination and applying the parameter into simulating radar bright band, it has been shown that, for a normal intense cloud echo such as 5874 mm6. m-3 （37.69 dBZ）, radar reflectivity factor can increase by 2. 57 times in case the conglutination percentage =33%, increase by 3.29 times in case p =50%, and increase by 5.59 times in case p=100%, respectively, while the increase is only increase by 2.40 times if the conglutina- tion is not considered. Therefore, conglutination on the edge of two spherical particles along radar wave polariza- tion direction can effectively increase the radar reflectivity factor and greatly benefit the formation of bright band.

关 键 词：粒子边缘粘连 后向散射 雷达反射率因子 0℃层亮带 

分 类 号：P435[天文地球—大气科学及气象学]