Shortwave, single‐scattering properties of arctic ice clouds
Shortwave, single‐scattering properties of arctic ice clouds
复制标题
北极冰云的短波、单散射特性
DOI：
10.1029/2000jd900195
复制
发表时间：
2001
影响因子：
--
通讯作者：
H. Gerber
中科院分区：
文献类型：
--
作者：
T. Garrett;P. Hobbs;H. Gerber
分析了云的不对称参数 (g) 和消光系数 (βext) 的首次直接机载测量。这些测量值是在 1998 年 5 月和 6 月在北极云中使用云积分浊度计 (CIN) 获得的。CIN 的评估是通过将其对水云单散射特性的测量值与使用液滴尺寸光谱测量值得出的米氏理论值进行比较来评估的。这些结果用于解释冰和混合相云的单散射特性的 CIN 测量。对于仅由冰晶组成的卷云，g 的导出值为 0.74±0.03（如果假设冰晶面完全光滑且平行，则为 0.76±0.03）；该值明显低于假设冰晶为六角棱柱或子弹花结时计算出的值。卷云 βext 的 CIN 测量值比冰晶横截面积和浓度测量值大几倍。讨论了对冰云的计算光学特性和测量光学特性之间差异的几种可能的解释。混合相云的 g 测量值取决于水和冰的相对浓度。这些结果用于表明云的反照率对冰形成的开始特别敏感。弱对流云和液态水饱和云的 g 值通常高于非对流云或冰饱和但液态水次饱和的云的 g 值。
The first direct airborne measurements of the asymmetry parameter (g) and extinction coefficient (βext) of clouds are analyzed. The measurements were obtained with a Cloud-Integrating Nephelometer (CIN) in arctic clouds in May and June 1998. The CIN was evaluated by comparing its measurements of the single-scattering properties of water clouds with values from Mie theory using measurements of the droplet size spectra. These results are used to interpret CIN measurements of the single-scattering properties of ice and mixed-phase clouds. For cirrus clouds composed solely of ice crystals the derived value of g was 0.74±0.03 (or 0.76±0.03 if ice crystal faces are assumed to be perfectly smooth and parallel); this value is significantly lower than that calculated assuming the ice crystals to be hexagonal prisms or bullet rosettes. The CIN measurements of βext for cirrus clouds were several times greater than values derived from measurements of the cross-sectional areas and concentrations of the ice crystals. Several possible explanations for the differences between calculated and measured optical properties of the ice clouds are discussed. The measured values of g for mixed-phase clouds depended on the relative concentrations of water and ice. These results are used to show that the albedo of clouds is particularly sensitive to the onset of ice formation. Weak convective clouds and clouds saturated with respect to liquid water generally had higher values of g than those for nonconvective clouds or clouds saturated with respect to ice but subsaturated with respect to liquid water.