Long-Term Statistics of Riming in Nonconvective Clouds Derived from Ground-Based Doppler Cloud Radar Observations
Long-Term Statistics of Riming in Nonconvective Clouds Derived from Ground-Based Doppler Cloud Radar Observations
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DOI：
10.1175/jas-d-20-0007.1
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发表时间：
2020-10
影响因子：
3.1
通讯作者：
S. Kneifel;D. Moisseev
中科院分区：
文献类型：
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作者：
S. Kneifel;D. Moisseev
日凌是一种将液态云水转化为冰的有效过程，在冷云中降水的形成中起着重要作用。由于冰粒质量的迅速增加，霜化提高了冰粒的终端速度，如果垂直空气运动的影响可以充分减轻，地面垂直指向云雷达可以检测到。在我们的研究中，我们首先回顾了以前发表的方法，雷达平均多普勒速度（MDV）雾凇质量分数（FR）使用大型地面原位数据集。这种关系，然后应用于多年的云雷达观测数据集收集在欧洲四个网站，包括污染的中欧，清洁的海洋，北极气候条件。我们发现，雾凇发生在1%-8%的非对流含冰云与中值FR在0.5和0.6之间。两个频率的riming和FR揭示相对较小的变化，不同的季节。与以前的研究相比，这表明清洁环境的增强riming，我们的统计数据表明相反;然而，位置之间的差异总体上很小。我们发现了一个非常强的关系之间的频率和温度的雾凇。虽然在低于−12°C的温度下很少出现结霜，但在接近0°C时会强烈增加。先前的研究发现，过冷液态水的量和液滴尺寸具有非常相似的温度依赖性，这可能与本研究中发现的riming签名密切相关。在相反的riming频率，我们发现几乎没有温度依赖性FR。
Riming is an efficient process of converting liquid cloud water into ice and plays an important role in the formation of precipitation in cold clouds. Due to the rapid increase in ice particle mass, riming enhances the particle’s terminal velocity, which can be detected by ground-based vertically pointing cloud radars if the effect of vertical air motions can be sufficiently mitigated. In our study, we first revisit a previously published approach to relate the radar mean Doppler velocity (MDV) to rime mass fraction (FR) using a large ground-based in situ dataset. This relation is then applied to multiyear datasets of cloud radar observations collected at four European sites covering polluted central European, clean maritime, and Arctic climatic conditions. We find that riming occurs in 1%–8% of the nonconvective ice containing clouds with median FR between 0.5 and 0.6. Both the frequency of riming and FR reveal relatively small variations for different seasons. In contrast to previous studies, which suggested enhanced riming for clean environments, our statistics indicate the opposite; however, the differences between the locations are overall small. We find a very strong relation between the frequency of riming and temperature. While riming is rare at temperatures lower than −12°C, it strongly increases toward 0°C. Previous studies found a very similar temperature dependence for the amount and droplet size of supercooled liquid water, which might be closely connected to the riming signature found in this study. In contrast to riming frequency, we find almost no temperature dependence for FR.