Ultraclean Layers and Optically Thin Clouds in the Stratocumulus-to-Cumulus Transition. Part II: Depletion of Cloud Droplets and Cloud Condensation Nuclei through Collision-Coalescence
Ultraclean Layers and Optically Thin Clouds in the Stratocumulus-to-Cumulus Transition. Part II: Depletion of Cloud Droplets and Cloud Condensation Nuclei through Collision-Coalescence
复制标题
层积云到积云转变中的超净层和光学薄云。
DOI：
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
C. Bretherton
中科院分区：
文献类型：
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作者：
O. Kuan;R. Wood;C. Bretherton
第一部分用飞机观测资料表明，海洋边界层（MBL）中的超净层（UCL）是东北太平洋层积云-积云过渡区（SCT）的一个共同特征。超净层被定义为云层或晴朗的空气层，其中直径大于0.1 μm的颗粒浓度低于10 cm-3。在这里，理想化的微物理包裹模拟表明，在积云制度，碰撞合并可以强烈地消耗在铜上升气流中的云滴浓度，从而从大气中去除云凝结核（CCN），这表明碰撞清除可能是造成低粒子浓度的关键过程在UCL。此外，模型的结果表明，层积云制度通常是不利于UCL的形成，因为冷凝物的量一般不足以耗尽下降的时间，它所需要的阁楼空气到上PBL。聚结尺度的批量参数化。
AbstractIn part I, aircraft observations are used to show that ultraclean layers (UCLs) in the marine boundary layer (MBL) are a common feature of the stratocumulus to cumulus transition (SCT) region over the NE Pacific. The ultraclean layers are defined as layers of either cloud or clear air in which the concentration of particles with diameter larger than 0.1 μm is below 10 cm-3. Here, idealized microphysical parcel modeling shows that in the cumulus regime, collision-coalescence can strongly deplete cloud droplet concentration in Cu updrafts thereby removing cloud condensation nuclei (CCN) from the atmosphere, suggesting that collision-scavenging is likely the key process causing the low particle concentration in UCLs. Furthermore, the model results suggest that the stratocumulus regime is typically not favorable for UCLs formation, because condensate amounts are generally not large enough to deplete drops in the time it takes to loft air to the upper PBL. A bulk parameterization of the coalescence-sca...