Increased rates of rainfall production in electrified clouds
Increased rates of rainfall production in electrified clouds
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带电云中降雨量的增加
DOI：
10.1002/qj.49709942223
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发表时间：
1973
影响因子：
8.9
通讯作者：
B. Vonnegut
中科院分区：
文献类型：
--
作者：
P. Brazier‐Smith;S. Jennings;J. Latham;C. Moore;B. Vonnegut
近年来，许多工作者，包括Sartor（1967）、Colgate（1967）和莱瑟姆（1969），研究了降雨产生的可能性，降雨产生的速度太快，不能用非带电云的碰撞和聚合效率来解释，可能是在强电场存在下收集效率或相互作用速率增加的结果。这些调查的结果一直是不确定的，虽然共识似乎是，场强必须接近崩溃的量级之前，显着的影响，云粒子的降水尺寸将产生。这种效应可能是冯内古特和摩尔（1960）以及摩尔等人所描述的降雨或冰雹现象的原因。(1962，1964年），这显然与雷击有关，但他们不能解释所报道的增加降水增长率的云包含弱得多的领域。在这篇文章中，我们重新审视了后一种现象的现有证据，试图明确地确定在没有电力的情况下，碰撞和聚结的传统微物理过程是否不能以所观察到的速率产生雨滴。1957年和1958年在新墨西哥州进行的田间试验（摩尔、冯内古特和博特卡（1958年）、摩尔和冯内古特（1960年）以及其他论文）和1951年至1956年在乌克兰干旱地区进行的田间试验（穆奇尼克，1965年）都证明了生长率增加。虽然Sartor已经表明，Muchnik报告的对流云中总凝结水的交换率对降水增长提出了严格的要求，而“非电”微物理学无法满足这一要求，但后者的信息不能被视为确定的。Muchnik的数据基本上包括使用地面雨量计网络获得的降水强度和持续时间的测量结果。上升气流速度，液态水含量，微物理和电气特性的补充测量，从雨量计数据得出的推论依赖于信息和相关方程从单独的研究，有时在不同的地方。因此，在缺乏对单个云的详细个案研究的情况下，任何基于穆奇尼克工作的对流云中雨滴增长率的计算都必须被视为高度投机。同样的批评不能适用于摩尔等人的研究，他们使用装有仪表的飞机、系留气球、雷达和其他地面设备，同时记录雷云在其整个生命周期中的微物理、电气和动力学发展。因此，有必要更详细地考虑他们的结果。他们关于带电云加速增长率的证据是基于1957年8月两天的观测。在第一次（8月13日），两次观察到直径3毫米的雨滴在云中降水形成后的几分钟内到达地面，正如他们的雷达所识别的那样，但在云中电场已经建立的阶段。8月16日也取得了类似的记录。根据马歇尔-帕尔默分布、0.5 gm m-3液态水含量和雷达设备的机载校准，估计的反射率中值水滴直径接近下午100点。由于雷达探测后雨滴穿过云层的最大下落时间分别为140、65和180 s，
In recent years many workers, including Sartor (1967)’Colgate (1967) and Latham (1969), have examined the possibility that the reported observations of rainfall production, which are too rapid to be explicable in terms of the accepted collision and coalescence efficiencies in nonelectrified clouds, may have been a consequence of increased collection efficiencies or interaction rates in the presence of strong electric fields. The results of these investigations have been inconclusive, although the concensus appears to be that the field-strength must be close to breakdown magnitudes before significant effects on cloud particles of precipitation dimensions will be produced. Such effects may possibly be responsible for the rain or hail-gush phenomena described by Vonnegut and Moore (1960) and Moore et al.(1962, 1964), which are clearly associated with lightning strokes, but they could not explain the reported increased growth rates of precipitation in clouds containing much weaker fields. In this note a re-examination of the existing evidence for this latter phenomenon is presented, in an attempt to establish definitively whether the conventional microphysical processes of collision and coalescence are incapable, in the absence of electrical forces, of producing raindrops at the observed rate. The evidence for increased growth rates emanates from field experiments conducted in New Mexico in 1957 and 1958 (Moore, Vonnegut and Botka (1958), Moore and Vonnegut (1960) and other papers) and in the arid regions of the Ukraine from 1951 to 1956 (Muchnik 1965). Although Sartor has shown that the rate of exchange of total condensed water in convective clouds reported by Muchnik places a severe requirement on precipitation growth that cannot be met by the ‘non-electrical’microphysics, the latter’s information cannot be regarded as definitive. Muchnik’s data consists essentially of measurements of precipitation intensity and duration obtained using a ground-based network of rain-gauges. No complementary measurements of the updraught velocities, liquid water contents, microphysical and electrical properties were made, and inferences drawn from the rain-gauge data depended upon information and correlative equations obtained from separate studies, sometimes in quite different localities. Consequently, in the absence of detailed case-studies of individual clouds, any calculations, based on Muchnik’s work, of the rates of growth of raindrops in convective clouds must be regarded as highly speculative. The same criticism cannot be applied to the studies of Moore et al. who used instrumented aircraft, tethered balloons, radar and other ground-based equipment to record simultaneously the microphysical, electrical and dynamical development of thunder clouds throughout their lifetime. It is necessary, therefore to consider their results in more detail.Their evidence for accelerated growth rates in electrified clouds was based on observations on two days in August 1957. On the first occasion,(13 August), it was twice observed that raindrops of diameter 3 mm reached the ground within a few minutes of the formation of precipitation within a cloud, as discerned by their radar, but at a stage when the electric field within the cloud was well established. A similar record was obtained on 16 August. The estimated median drop diameter for reflectivity, based on a Marshall-Palmer distribution, 0.5 gm m-3 liquid water content and airborne calibration of their radar equipment, was close to 100 pm. Since the estimated maximum times of fall of the raindrops through the cloud after radar detection were 140, 65 and 180 s respectively for the three cases, and since …