Crystal Growth in Ice Clouds at Low Temperatures

这笔赠款支持研究高卷云和极地平流层云(PSCS)所特有的低温和高压条件下冰晶的成核、习性和生长。这是哈莱特博士和他的同事们多年来在不那么极端的条件下所做的冰晶物理研究的继续。之前的工作中使用的静态扩散室将被改装，以使其工作温度降至零下100摄氏度，压力低于100 mb。在小室中，晶体生长在薄的(5-10微米)玻璃丝上，在温度、压力和过饱和的控制条件下。晶体的成核和生长在室内用光学显微镜观察，并进行录像。在插入腔室之前，可能的核素将被加入灯丝中。这些物质包括不挥发的可溶颗粒，如硫酸，以及不溶矿物、陨石和飞机尾气材料。寒冷的高空云对太阳和红外辐射的传输有重要影响，因此对全球气候也有重要影响。它们还在臭氧的产生和破坏中发挥作用。尽管它们很重要，但这些云的物理性质并不为人所知，因为在大多数飞机天花板以上的高度进行现场测量是困难的。该项目的实验室实验将模拟极端的大气条件，并提供有关云的微物理特征的必要信息，这些信息几乎无法通过其他手段获得。

This grant supports research on the nucleation, habit, and growth of ice crystals under the low temperature and pressure conditions characteristic of high cirrus clouds and polar stratospheric clouds (PSCs). It is a continuation of work on the physics of ice crystals that Dr. Hallett and his colleagues have done for many years for less extreme conditions. The static diffusion chamber used in previous work will be modified to operate down to temperatures as cold as -100C and pressures less than 100 mb. In the chamber crystals are grown on thin (5-10 microns) glass filaments under controlled conditions of temperature, pressure, and supersaturation. Crystal nucleation and growth are examined by optical microscopy from outside the chamber and video recorded. Likely nucleants will be added to the filament prior to insertion in the chamber. These include nonvolatile soluble particles, such a sulfuric acid, as well as insoluble mineral, meteoritic, and aircraft exhaust material. Cold, high-altitude clouds have important effects on the transfer of solar and infrared radiation, and hence global climate. They also play a part in the production and destruction of ozone. In spite of their importance, the physical properties of these clouds are not well known because of the difficulty of in situ measurements at heights above the ceiling of most aircraft. The laboratory experiments on this project will simulate the extreme atmospheric conditions and provide needed information on the microphysical characteristics of clouds which are nearly inaccessible by other means.