Some outstanding problems in cloud physics – the interaction of microphysical and dynamical processes
Some outstanding problems in cloud physics – the interaction of microphysical and dynamical processes
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云物理中的一些突出问题——微物理与动力学过程的相互作用
DOI：
10.1002/qj.49709540502
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发表时间：
1969
影响因子：
8.9
通讯作者：
B. J. Mason
中科院分区：
文献类型：
--
作者：
B. J. Mason
云物理学一方面关注云系统的结构和演变，另一方面关注云和降水要素形成和增长所涉及的物理过程，它是沿着两条相当独立的路线构想和发展的。物理学家和物理化学家主要在实验室里研究水蒸气凝结形成水滴的微物理过程，水滴的过冷、成核和冻结，雪晶的生长和聚集，雨滴、雪花和冰雹形成的详细机制，以及云的各种起电过程。相反，空气运动的运动学、动力学和观测研究，控制着云的形成、生长、尺寸、形状、组织、寿命和活力，一直是气象学家关注的主要问题。鉴于这两种方法所需要的背景和技术的不同，这种二分法可能是不可避免的，但不幸的是。由于对空气运动和微物理事件之间的相互关系认识不清，进展受到阻碍，而微物理事件协同作用，最终导致降水的释放。当然，是云层内部和云层周围的空气运动，再加上充当凝结核和冻结核的气溶胶的特性，决定了云粒子的浓度、初始大小分布和物理性质。一旦这些形成，凝结和聚集的微物理过程就开始扩大颗粒大小的范围，水成物的产生现在正在进行中。因为空气的运动决定着云的大小、含水量和持续时间，所以它不仅控制着这些过程的速率，还控制着这些过程运行的时间，从而决定了粒子能达到的最大尺寸。如果出现降水，同样是空气运动决定了降水的分布、强度和持续时间。相反，粒子群的生长和蒸发，伴随着相和水浓度的变化，提供了可以深刻影响空气运动的热源和汇。因此，在云滴生长和冻结过程中，潜热的释放通过为云提供额外的浮力，可以促进和维持云的生长，直到上升气流被破坏，或者通过与干燥的环境混合，或者通过凝结水的积累和形成由降水蒸发维持的下降气流。
Cloud physics, being concerned on the one hand with the structure and evolution of cloud systems and, on the other, with the physical processes involved in the formation and growth of cloud and precipitation elements, has been conceived and developed along two rather separate lines. The microphysical processes of condensation of water vapour to form droplets, the supercooling, nucleation and freezing of water droplets, the growth and aggregation of snow crystals, the detailed mechanisms of raindrop, snowflake and hailstone formation, and the various processes of cloud electrification, have been mainly investigated by physicists and physical chemists in the laboratory. Obversely, kinematical, dynamical and observational studies of the air motions, which govern the formation, growth, dimensions, shape, organization, life-time and vigour of the clouds, have been mainly the concern of meteorologists. This dichotomy, though probably inevitable in view of the differences in background and technique required by the two approaches, has nevertheless been unfortunate. Progress has been hindered by a poor appreciation of the interrelations between the air motions and the microphysical events which, acting in concert, culminate in the release of precipitation.It is, of course, the air motions in and around the clouds, in combination with the properties of the aerosols that act as condensation and freezing nuclei, that determine the concentration, initial size distribution, and physical nature of the cloud particles. As soon as these have formed, the microphysical processes of condensation and aggregation begin to broaden the particle-size spectrum and the production of hydrometeors is now under way. Because the air motion governs the dimensions, water content, and duration of the cloud, it controls not only the rates of these processes, but the period over which they operate and thus the maximum size which the particles can attain. If precipitation should result, it is again the air motion which determines its distribution, intensity and duration. Conversely, the growth and evaporation of particle populations, accompanied by changes of phase and water concentration, provide sources and sinks of heat that can profoundly influence the air motion. Thus the release of latent heat during the growth and freezing of cloud droplets, by providing additional buoyancy to the cloud, may promote and sustain its growth until the updraught is destroyed, either by mixing with the drier surroundings, or by accumulation of condensed water and the formation of a downdraught sustained by evaporation of the precipitation.