On the microphysical effects of observed cloud edge charging
On the microphysical effects of observed cloud edge charging
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DOI：
10.1002/qj.2554
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发表时间：
2015-10-01
影响因子：
8.9
通讯作者：
Ambaum, M. H. P.
中科院分区：
文献类型：
--
作者：
Harrison, R. G.;Nicoll, K. A.;Ambaum, M. H. P.
全球范围内液体层云非常丰富。由于缺乏强对流，它们不会通过不同阶段的水成物之间碰撞带电的通常雷暴机制而带电。相反，晴朗天气下的背景全球电路电流在很大程度上不受层云存在的影响，并且，如果层云在水平方向广泛分布，则垂直方向的晴朗天气传导电流通过云。垂直电流流动的一个结果是，在云和空气的边界，那里有一个电导率的转变，液滴形成或蒸发，液滴充电发生。电荷对液滴蒸发和液滴碰撞都有影响。利用新的无线电探空仪器，在层云边缘观测到的电荷对这两种微物理液滴过程进行了评估。这表明，对于小液滴来说，充电比激活更有可能影响碰撞过程。提高小液滴的收集效率改变了小液滴的演化和通过粒径分布传播，缩短了小液滴到雨滴的自转化时间尺度，改变了云的辐射特性。由于传导电流密度受到外部（如太阳对高能粒子的调制）和内部（如厄尔尼诺-南方涛动）因素的影响，导致层云边缘充电的电流为表达太阳对气候系统的影响提供了可能的途径，也为传达内部气候变率提供了遥相关机制。
Liquid layer clouds are abundant globally. Lacking strong convection, they do not become electrified by the usual thunderstorm mechanisms of collisional electrification between hydrometeors of different phases. Instead, the background global circuit current flow in fair weather is largely unaffected by the layer cloud's presence, and, if the layer cloud is extensive horizontally, the vertical fair weather conduction current passes through the cloud. A consequence of the vertical current flow is that, at the cloud-air boundary where there is a conductivity transition and droplets form or evaporate, droplet charging occurs. Charge can affect both droplet evaporation and droplet-droplet collisions. Using new radiosonde instrumentation, the charge observed at layer cloud edges is evaluated for both these microphysical droplet processes. This shows that the charging is more likely to affect collision processes than activation, for small droplets. Enhancing the collection efficiency of small droplets modifies their evolution and propagates through the size distribution to shorten the autoconversion time-scale to rain drops, and the cloud radiative properties. Because the conduction current density is influenced by both external (e.g. solar modulation of high-energy particles) and internal (e.g. El Nino-Southern Oscillation) factors, current flow leading to layer cloud edge charging provides a possible route for expressing solar influences on the climate system and a teleconnection mechanism for communicating internal climate variability.