中文摘要：

冰水含量在气候以及天气变化、人工影响天气等方面的研究中具有重要影响。毫米波雷达在探测卷云时由于气流运动等因素的影响使得电磁波照射体积内粒子自身发生旋转运动,这为精确计算粒子散射截面以及利用其散射特性反演云中冰水含量造成困难。首先给出六种常见的非球形冰晶粒子模型,利用HFSS软件讨论特定尺寸下非球形粒子及其等效球形粒子的辐射方向图差异,利用矩量法（针对非球形粒子）以及洛伦兹-米理论（针对球形粒子）计算并拟合上述冰晶粒子在静止、水平旋转以及随机旋转三种取向下最大尺寸与后向散射截面之间的双指数关系式,假定卷云冰晶粒子混合模型满足B-H模型,云粒子的谱分布服从NASA在2007年实测的指数分布,计算出实际的冰水含量,讨论了三种取向下非球形粒子及等体积球粒子群的雷达反射率因子Z,将其代入常用的IWC-Z关系式,结果表明利用雷达反射率因子反演冰水含量时必须考虑高空风产生的粒子取向问题,等效球理论方法得到的冰水含量比实际值偏小,该结论对于毫米波雷达精确反演卷云的微观物理参数具有重要意义。

英文摘要：

Ice water content （IWC） has an important influence on climate change, weather change, weather modification etc. When a millimeter wave radar detects cirrus, particles rotate due to air motion, making hack- scattering cross sections inaccurately computed and as a result influencing the IWC which is determined by them. In this paper, models of six non-spherical ice particles were described first and their radiation patterns at specific sizes were then simulated by HFSS software in order to disscuss the difference between different orienta- tion and equivalent spheres. For the case of three different orientations （fixed orientation, horizontal orientation, random orientation）, the double-exponential function relationships between particles＇ maximum size and backscattering cross sections were fitted based on the scattering results of non-spherical ice paritlcles computed by Method of Moment and those of equivalent spherical particles computed by Lorenz-mie theory. Assuming that the mixture of non-spherical ice particles meets the B-H mixing model and the size distribution of cirrus obeys the exponential distribution, which is measured by NASA in 2007, the fixed IWC of cirrus is computed which meets the above two conditions, and radar reflectivities of nonspherical ice paritcles and equivalent spheres at three different orientations, based on the above assumption, also can be computed, which were then put into the known formula IWC-Z to get different results of IWC. The anlysis shows that orientation must be considered when retrieving IWC using radar reflectivity Z, because the IWC retrieved by the equivalent sphere theory would underestimate the actual IWC. These results are significant in accurate retrieving micro-physical parameters of cirrus.