In this paper, unprecedented bulk measurements of ice water content (IWC) up to approximately 5 g m(-3) and 95-GHz radar reflectivities Z(95) are used to analyze the statistical relationship between these two quantities and its variability. The unique aspect of this study is that these IWC-Z(95) relationships do not use assumptions on cloud microphysics or backscattering calculations. IWCs greater than 2 g m(-3) are also included for the first time in such an analysis, owing to improved bulk IWC probe technology and a flight program targeting high ice water content. Using a single IW-Z(95) relationship allows for the retrieval of IWC from radar reflectivities with less than 30% bias and 40%-70% rms difference. These errors can be reduced further, down to 10%-20% bias over the whole IWC range, using the temperature variability of this relationship. IWC errors largely increase for Z(95) > 16 dBZ, as a result of the distortion of the IWC-Z(95) relationship by non-Rayleigh scattering effects. A nonlinear relationship is proposed to reduce these errors down to 20% bias and 20%-35% rms differences. This nonlinear relationship also outperforms the temperature-dependent IWC-Z(95) relationship for convective profiles. The joint frequency distribution of IWC and temperature within and around deep tropical convective cores shows that at the -50 degrees +/- 5 degrees C level, the cruise altitude of many commercial jet aircraft, IWCs greater than 1.5 g m(-3) were found exclusively in convective profiles.
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机译:在本文中,对高达5 g m(-3)的冰水含量(IWC)和95-GHz雷达反射率Z(95)进行了前所未有的批量测量,以分析这两个量之间的统计关系及其可变性。这项研究的独特之处在于,这些IWC-Z(95)关系并未使用云微物理学或反向散射计算的假设。由于改进的散装IWC探针技术和针对高冰水含量的飞行计划,这种分析中还首次包括大于2 g m(-3)的IWC。使用单个IW-Z(95)关系可以从雷达反射率中检索IWC,偏差小于30%,均方根差为40%-70%。利用这种关系的温度可变性,可以进一步降低这些误差,在整个IWC范围内将误差降低至10%-20%。由于非瑞利散射效应引起的IWC-Z(95)关系的失真,对于Z(95)> 16 dBZ,IWC误差会大大增加。提出了一种非线性关系,以将这些误差减小到20%的偏差和20%-35%的均方根值差异。这种非线性关系也优于对流剖面的温度相关的IWC-Z(95)关系。 IWC和深热带对流核心内部及其周围温度的联合频率分布表明,在-50度+/- 5摄氏度的水平下,许多商用喷气飞机的巡航高度被发现,IWC大于1.5 gm(-3)仅在对流剖面中。
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