An Experimental Study of Ice Crystal Growth and Evaporation

大气中冰晶通过气相沉积生长和蒸发收缩的物理机制是复杂的，而且仍然不确定。然而，晶体与其周围环境之间的蒸汽交换是冰相演化的核心。气相沉积确定了粒子的初始形状、质量和下落速度，因此与其他云粒子相互作用和降水形成所需的时间变得重要。冰晶的蒸发决定了卷云在衰变阶段的寿命。本项目是在受控的实验室条件下，在适合自由大气条件的温度、压力和湿度范围内，对单个冰晶的生长和蒸发进行实验研究。实验采用电平衡的方法使单个粒子在受控环境中悬浮。此外，还有使空气通过腔室的规定，以研究通风对晶体生长的影响。该研究将揭示晶体界面上的蒸汽交换，并提供所需的信息，以改进云发展和多云大气中化学物质输送的数值模型中晶体生长的参数化。

The physical mechanisms by which ice crystals in the atmosphere grow by vapor deposition and shrink by evaporation are complicated and still uncertain. Yet the exchange of vapor between a crystal and its environment is central for ice-phase evolution. Vapor deposition establishes the initial shapes, masses, and fallspeeds of the particles and hence the time needed for interactions with other cloud particles to become important and for precipitation to form. Evaporation of ice crystals determines the lifetime of cirrus clouds in their decaying stage. This project is an experimental study of the growth and evaporation of individual ice crystals in controlled, laboratory conditions, over a range of temperature, pressure, and humidity appropriate for conditions in the free atmosphere. The experiments employ the method of electrodynamic balance for levitating individual particles in a controlled environment. In addition, there is provision for moving the air through the chamber to study the effects of ventilation on crystal growth. The research will shed new light on vapor exchange at a crystal interface and provide the information needed to improve the parameterization of crystal growth in numerical models of cloud development and the transport of chemical species in cloudy atmospheres.