On the influence of electrostatic charging on coagulation of dust and ice particles in the upper mesosphere
On the influence of electrostatic charging on coagulation of dust and ice particles in the upper mesosphere
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静电充电对中层上部尘埃和冰粒凝结的影响
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
G. Reid
中科院分区：
文献类型：
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作者：
G. Reid
在高度约80公里以上的中间层上层，是大气层中发生大部分流星物质消融的区域，被认为含有微小的纳米尺寸的烟雾和尘埃颗粒，浓度为每立方厘米数千个。在高纬度极冷的夏季条件下，这些粒子可能形成凝结核，冰粒在凝结核上生长，从而产生各种独特的现象，包括冰粒云和局部电子耗尽（“咬蚀”）。最近的研究表明，这些粒子通过清除背景电离层中的自由电子和正离子而带电。在正常的白天条件下，电荷平衡的计算表明，大多数颗粒将携带单个负电荷，并且已经指出，静电排斥将抑制颗粒的凝聚，否则这将是它们生长的重要机制。这里表明，当电离率非常低时，例如在没有高能粒子沉淀的夜晚，情况正好相反。在这种情况下，带正电和带负电的颗粒倾向于以相等的数量存在，并且通过充电来增强凝结，而不是被抑制。由于影响凝血的除充电以外的主要未知因素，只能对凝血速率进行理想化的半定量估计。然而，充电似乎是一个不太严重的障碍，凝血比以前认为的，实际上可能是一个强大的刺激。
The upper mesosphere, at heights above about 80 km, is the region of the atmosphere in which most ablation of incoming meteoric material takes place, and is thought to contain tiny nanometer‐size smoke and dust particles with concentrations of several thousand per cubic centimeter. In the extremely cold summer conditions at high latitudes, these particles probably form the condensation nuclei on which ice particles grow, giving rise to a variety of unique phenomena, including noctilucent clouds and localized electron depletions (“biteouts”). Recent work has shown that the particles become electrically charged by scavenging free electrons and positive ions from the background ionosphere. Under normal daytime conditions, calculations of charge balance have shown that most of the particles will carry a single negative charge, and it has been pointed out that electrostatic repulsion will inhibit coagulation of the particles, which would otherwise be an important mechanism for their growth. It is shown here that the opposite is true when ionization rates are very low, for example at night in the absence of energetic‐particle precipitation. In this case, positively and negatively charged particles tend to exist in equal numbers, and coagulation is enhanced by charging, instead of being inhibited. Because of the major unknown factors other than charging that affect coagulation, only idealized semi‐quantitative estimates of coagulation rates can be made. Electrical charging, however, appears to be a much less serious barrier to coagulation than had been thought, and may actually be a powerful stimulant.