Shear-induced electrical changes in the base of thin layer-cloud
Shear-induced electrical changes in the base of thin layer-cloud
复制标题
薄层云底部剪切引起的电变化
DOI：
10.1002/qj.3648
复制
发表时间：
2019
影响因子：
8.9
通讯作者：
Harrison R
中科院分区：
文献类型：
--
作者：
Harrison R
广泛的层状云的上下水平边界的充电是由全球电路中的电流引起的。层云电荷积累以前被认为是一种纯粹的静电现象，但它并不是孤立于气象过程而发生的，气象过程可以传输电荷。薄层云为研究这种动态电荷传输提供了特殊的环境，因为云顶的破坏可能会到达云底，从表面可以观察到。在这里，观察到一个薄的（约300米）持续层云，底部在300米处，云顶有强风切变，云底高度、光学厚度和下面的表面电位梯度（PG）产生强烈相关的波动。PG变化被确定为先于云底波动2分钟，这与切变引起的云顶电变化以及随后的云底变化一致。这些观测结果首次证明了层云内电荷的动态驱动修改。即使在弱电荷层云中，电荷的重新分布也会改变云中的局部电场和相互作用的带电云滴的碰撞行为。局部场增强也可以解释先前在暖云中观察到的静电放电。
Charging of upper and lower horizontal boundaries of extensive layer‐clouds results from current flow in the global electric circuit. Layer‐cloud charge accumulation has previously been considered a solely electrostatic phenomenon, but it does not occur in isolation from meteorological processes, which can transport charge. Thin layer‐clouds provide special circumstances for investigating this dynamical charge transport, as disruption at the cloud‐top may reach the cloud base, observable from the surface. Here, a thin (∼300 m) persistent layer‐cloud with base at 300 m and strong wind shear at cloud‐top was observed to generate strongly correlated fluctuations in cloud base height, optical thickness and surface electric Potential Gradient (PG) beneath. PG changes are identified to precede the cloud base fluctuations by 2 min, consistent with shear‐induced cloud‐top electrical changes followed by cloud base changes. These observations demonstrate, for the first time, dynamically driven modification of charge within a layer‐cloud. Even in weakly charged layer‐clouds, redistribution of charge will modify local electric fields within the cloud and the collisional behaviour of interacting charged cloud droplets. Local field intensification may also explain previously observed electrostatic discharges in warm clouds.