Accurate determination of thermodynamic cloud phase is critical for establishing the radiative impact of clouds on climate and weather. Depolarization of the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) 532 nm signal provides a useful addition to other methods of thermodynamic phase discrimination that rely on temperature, cloud top altitude or a temperature-based cloud phase climatology. Active detection of the thermodynamic phase of multiple cloud layers in a vertical column using cloud layer-integrated depolarization and backscatter also alleviates ambiguities in cloud phase determination by passive radiometers. The CALIOP phase algorithm primarily uses vertically integrated cloud layer depolarization and attenuated backscatter to determine the dominant thermodynamic phase of hydrometeors present in a cloud layer segment, at horizontal resolutions for cloud layer detection varying between 333 m and 80 km, with cloud layer vertical resolutions between 60 m and 8 km. CALIOP ice cloud backscatter observations taken with a 0.3^∘ near-nadir view between June 2006 and November 2007 include a significant amount of specular reflection from hexagonal smooth crystal faces that are oriented perpendicularly to the incident lidar beam (horizontally oriented ice – HOI). These specular reflections from HOI are shown here to occur between 0 and −40 ^∘C, with a peak in the CALIOP distribution observed globally at −15 ^∘C. Recent viewing angle testing occurring during 2017 at 1, 1.5 and 2^∘ and reported here quantifies the impact of changing the viewing angle on these specular reflections and verifies earlier observations by POLDER. These viewing angle tests show that at the −15 ^∘C peak of the HOI distribution the mean backscatter from all ice clouds decreases by 50 % and depolarization increases by a factor of 5 as the viewing angle increases from 0.3 to 3^∘. To avoid these specular reflections, the CALIOP viewing angle was changed from 0.3 to 3^∘ in November 2007, and since then CALIOP has been observing clouds almost continuously for 12–13 more years. This has provided more data for a thorough re-evaluation of phase determination and has motivated changes to the CALIOP cloud phase algorithm for Version 4 (V4). The V4 algorithm now excludes over-identification of HOI at 3^∘, particularly in cold clouds. The V4 algorithm also considers cloud layer temperature at the 532 nm centroid and has been streamlined for more consistent identification of water and ice clouds. In V4 some cloud layer boundaries have changed because 532 nm layer-integrated attenuated backscatter in V4 has increased due to improved calibration and extended layer boundaries, while the corresponding depolarization has stayed about the same. There are more V4 cloud layers detected and, combined with increasing cloud edges, the V4 total atmospheric cloud volume increases by 6 %–9 % over V3 for high-confidence cloud phases and by 1 %–2 % for all cloudy bins. Collocated CALIPSO Imaging Infrared Radiometer (IIR) observations of ice and water cloud particle microphysical indices complement the CALIOP ice and water cloud phase determinations.

中文翻译：

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CALIOP V4云的热力学相分配和近天底视角的影响

准确确定热力学云相对于确定云对气候和天气的辐射影响至关重要。正交偏振（CALIOP）532 nm的云气激光雷达的去极化 信号为依赖温度，云顶高度或基于温度的云相气候的其他热力学相判别方法提供了有用的补充。使用集成了云层的去极化和反向散射对垂直柱中多个云层的热力学相进行主动检测，还可以减轻无源辐射计确定云相的不确定性。CALIOP阶段算法主要使用垂直整合的云层去极化和衰减的反向散射来确定云层段中存在的水凝物的主要热力学相，水平分辨率在333 m和80  km之间变化 ，而云层垂直分辨率在60 米和8 公里。用0.3采取CALIOP冰云反向散射的观测^∘ 2006年6月和2007年11月之间的近天底视图包括由六方平滑晶面被定向为垂直于入射激光雷达波束（水平定向的冰- HOI）镜面反射的显著量。从这些HOI的镜面反射在此示出0和之间发生-40  ^∘ Ç，随着CALIOP分布的峰，在全球范围内观察到-15  ^∘ Ç。最近的视角测试发生在2017年的1、1.5和^2∘并在此报道了量化视角变化对这些镜面反射的影响，并验证了POLDER的早期观察结果。这些视角的测试表明，在-15  ^∘ Ç由5从0.3视角增大的一个因素的分布HOI从所有冰云的平均反向散射由50度％和去极化的增大而减小的峰至3 ^∘。为了避免这些镜面反射，所述CALIOP视角由0.3改为3 ^∘从2007年11月开始，从那时起，CALIOP几乎连续观测云了12-13年。这为彻底重新评估相位确定提供了更多数据，并促使对版本4（V4）的CALIOP云相位算法进行了更改。的V4算法现在排除过识别HOI中的3 ^∘，特别是在冷云。V4算法还考虑了532 nm重心处的云层温度， 并且已进行了简化以更一致地识别水和冰云。在V4中，由于532 nm，一些云层边界已更改 由于改进的校准和扩展的层边界，V4中的层积分衰减后向散射有所增加，而相应的去极化几乎保持不变。检测到更多的V4云层，再加上云边缘增加，对于高置信度云阶段，V4总大气云量比V3增加了6％–9％，对于所有阴天区，其增加了1％–2％。并置的CALIPSO成像红外辐射仪（IIR）对冰和水云颗粒微物理指标的观察补充了CALIOP冰和水云相的测定。