An Experimental Study of Ice Crystal Growth and Evaporation

大气中的冰晶通过气相沉积生长和通过蒸发收缩的物理机制是复杂的，仍然不确定。然而，晶体与其环境之间的水蒸气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，从而确定了与其他云粒子相互作用变得重要和形成降水所需的时间。冰晶的蒸发决定了处于衰败阶段的卷云的寿命。该项目是在可控的实验室条件下，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的实验研究。实验采用电动平衡的方法将单个颗粒悬浮在受控环境中。此外，为了研究通风对晶体生长的影响，还提供了通过气室的空气流动的规定。这项研究将为晶体界面上的水蒸气交换提供新的线索，并提供必要的信息，以改进云发展和云大气中化学物质传输的数值模式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.