Doppler lidar measurements of oriented planar ice crystals falling from supercooled and glaciated layer clouds
Doppler lidar measurements of oriented planar ice crystals falling from supercooled and glaciated layer clouds
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DOI：
10.1002/qj.528
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发表时间：
2009-06
影响因子：
8.9
通讯作者：
C. Westbrook;A. Illingworth;E. O'connor;R. Hogan
中科院分区：
文献类型：
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作者：
C. Westbrook;A. Illingworth;E. O'connor;R. Hogan
利用垂直指向的多普勒激光雷达研究了平面冰晶水平沉降的特性。从它们定向的基面上观察到了强烈的镜面反射，通过与距离天顶4°的第二个激光雷达进行比较来识别。对17个月连续高分辨率观测的分析表明，这些原始晶体经常出现在从中层混合相层云落下的冰中(在−15°C的层中，85%的时间是这样的)。对一个案例的详细分析表明，晶体在过冷层内成核并迅速生长，然后脱落，形成明确的镜面反射层。仅从激光雷达无法量化定向晶体的比例，但偏振雷达测量证实，相当大一部分晶体群体具有良好的定向。当晶体落入亚饱和空气中时，镜面反射被观察到关闭，因为晶体表面变得圆润，失去了它们的刻面结构。
The properties of planar ice crystals settling horizontally have been investigated using a vertically pointing Doppler lidar. Strong specular reflections were observed from their oriented basal facets, identified by comparison with a second lidar pointing 4° from zenith. Analysis of 17 months of continuous high‐resolution observations reveals that these pristine crystals are frequently observed in ice falling from mid‐level mixed‐phase layer clouds (85% of the time for layers at −15 °C). Detailed analysis of a case study indicates that the crystals are nucleated and grow rapidly within the supercooled layer, then fall out, forming well‐defined layers of specular reflection. From the lidar alone the fraction of oriented crystals cannot be quantified, but polarimetric radar measurements confirmed that a substantial fraction of the crystal population was well oriented. As the crystals fall into subsaturated air, specular reflection is observed to switch off as the crystal faces become rounded and lose their faceted structure.