摘要:
本文讨论了Г(D)函数n(D)=ADαe-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D1、均方根直径D2、均立方根直径D3的比值k1=D1/D2、k2=D2/D3求取α的关系，进而可求出Г(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k1、k2求得的参数α1、α2多数是接近的，可以用一个介于α1～α2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D1、D2、D3、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。
Abstract:
In the Paper, Γ–distribution [n(D)=ADea-λD] parameters (A, a, λ) are obtained by the ratio k1=D1/D2, k2=D2/D3 and linear regression method, where D1, D2 and D3 are diameters for average, root mean square and root mean cube, respectively. The statistical data analysis of raindrop size distribution measured with OAP–2D–P show that the parameter 1 is usually close to 2 obtained from k1 and k2, respectively, so, value between 1 and 2 can be used to approach to it. We have chosen =2, n(D)= AD2e-λD are used to fit into observational raindrop spectra, which is more accuracy than Marshal-Palmer formular (=0). Thus, the regression coefficients (R), characteristic diameters (D1, D2, D3), number concentrations (N), rain rates (I ) and radar echo reflectivity (Z) are all more approximate to observational raindrop spectra than those from the two parameters
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