冰云光学特性与等效球Mie理论的误差分析

OPTICAL PROPERTIES OF ICE CLOUDS AND ERROR ANALYSIS UNDER MIE THEORY OF EQUIVALENT SPHERES

用改进的射线光学理论和等效球Ｍｉｅ理论，计算了若干冰晶和冰晶尺度分布在太阳光谱区中一系列波长上的光学特性和散射特性，详细分析了Ｍｉｅ散射计算的误差，并假定冰云光学特性有１０％误差的情况下，用Ｄｅｌｔａ－Ｅｄｄｉｎｇｔｏｎ近似对所引起的冰云辐射特性的误差进行了数值试验。结果表明，沿用已久的等效球Ｍｉｅ理论因计算冰云光学特性在波长小于２．６μｍ波段误差过大，将引起冰云辐射特性有显著误差，最后提出了计算冰云光学特性的新方案。

The optical properties of the single hexagonal ice crystals with different aspect ratios and ice clouds with different particle size distributions are calculated by using the improved ray optical theory and Mie scattering theory at some wavelengths located in the solar spectral region.The errors caused by Mie theory for the single sactering calculations are analysed in detail.Assuming the single scattering calculations with 10% errors,the caused errors for radiative transfer properties of ice clouds are examined using Delta Eddington approximation.The results show that the Mie scattering calculations at the region of λ <2.6μm have large errors for the opticala properties of ice clouds.Therefore the caused errors for the cloud radiative properties is significant.Finally,the schemes for calculations of the optical properties of ice clouds are proposed.