对流层下部雨滴谱分布

RAINDROP PARTICLE SIZE DISTRIBUTION IN THE LOWER TROPOSPHERE

本文讨论了Γ(D)函数 n(D)=AD~αe^(-λD)一阶、二阶、三阶原点矩与分布参数λ、α的关系。得出由实测雨滴谱算术平均直径 D_1、均方根直径 D_2、均立方根直径 D_3的比值 k_1=D_1/D_2、k_2=D_2/D_3求取α的关系,进而可求出Γ(D)函数的其它参数 A、λ。通过机载二维降水粒子探头(2D-P)获得的空中雨滴谱资料计算表明:由 k_1、k_2求得的参数α_1、α_2多数是接近的,可以用一个介于α_1～α_2的值α来近似。本文选取α=2对实测值进行拟合,并和广泛采用的 Marshal-Palmer 公式(α=0)进行了比较。结果表明:用α=2拟合不仅相关系数R、相关显著水平 K 较α=0拟合的对应值有明显提高,而且拟合的特征值,如 D_1、D_2、D_3、雨水含量 Q、雷达反射率因子 Z 都更接近于实测值,即用三参数(A、α、λ)来表征雨滴谱比双参数(A、λ)要精确得多。

In the paper,Γ—distribution[n(D)=ADe^(α-λD)]parameters(A,α,λ)are obtained by the ratio k_1=D_1/D_2,k_2=D_2/D_3 and linear regression method,where D_1,D_2,and D_3 are diameters for aver-age,root mean square and root mean cube,respectively.The statistical data analysis of raindrop size distribution measured with OAP—2D—P showthat the parameter α_1 is usually close to α_2 obtained from k_1 and k_2,respectively,so,value αbetween α_1 and α_2 can be used to appproach to it.We have chosen α=2,n(D)=AD^2e^(-λD)areused to fit into observational raindrop spectra,which is more accuracy than Marshal—Palmerformular(α=0).Thus,the regression coefficients(R),characteristic diameters(D_1,D_2,D_3),num-ber concentrations(N),rain rates(Ⅰ)and radar echo reflectivity(Z)are all more approximate toobservational raindrop spectra than those from the two parameters.