Enhancement of cloud formation by droplet charging
Enhancement of cloud formation by droplet charging
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通过液滴充电增强云的形成
DOI：
10.1098/rspa.2008.0009
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
M. Ambaum
中科院分区：
文献类型：
--
作者：
R. Harrison;M. Ambaum
电荷通过降低雾滴开始生长的最小过饱和度来影响云滴的活化。虽然所需的液滴电荷，以提高激活是相当大的，我们表明，足够的充电发生在云层的边缘，因为在全球大气电路中的公平天气电流流过电导率的不连续性。我们的理论预测，液滴中和将导致云底的瞬态冷却。这一假设在极端太阳活动期间得到了验证，当时我们在云层下面的表面检测到了瞬时电流爆发。我们将这些归因于离子产生的爆发，这将导致云中短暂的液滴中和和液滴临界过饱和度的相关增加。我们观察到的瞬态下降，在向下的长波辐射测量与瞬态电流爆发一致。由于穿过层状云的垂直电流密度是一种全球性现象，因此在许多地区都可能发生电荷增强效应对云形成的影响;我们发现，在当今气候中，电荷增强激活对表面辐射的影响可能高达0.1 W m−2。
Charge affects the activation of cloud droplets by reducing the minimum supersaturation at which haze droplets begin to grow. Although the droplet charge required to enhance activation is substantial, we show that sufficient charging occurs at the edges of layer clouds because the fair-weather current in the global atmospheric electrical circuit flows through a discontinuity in conductivity. Our theory predicts that droplet neutralization will cause a transient cooling of cloud base. This hypothesis was tested during a period of extreme solar activity, when we detected transient current bursts at the surface beneath a layer of cloud. We attribute these to bursts of ion production, which would cause transient droplet neutralization in the cloud and an associated increase in droplet critical supersaturation. We observed transient decreases in downward long-wave radiation measurements coincident with the transient current bursts. As the vertical current density passing through stratiform clouds is a global phenomenon, there are many regions in which a charge enhancement effect on cloud formation can potentially occur; we find that the effect of charge-enhanced activation on surface radiation in the present-day climate could be as large as 0.1 W m−2.