Crystal Growth in Ice Clouds at Low Temperatures

该基金支持在高卷云和极地平流层云（PSC）的低温和低压条件下冰晶的成核，习性和生长的研究。 这是哈雷特博士和他的同事们多年来在不那么极端的条件下对冰晶物理学所做工作的延续。 将对以前工作中使用的静态扩散室进行修改，使其工作温度低至-100 ℃，压力低于100 mb。 在腔室中，晶体在温度、压力和过饱和度的受控条件下在薄（5-10微米）玻璃丝上生长。 晶体成核和生长通过光学显微镜从腔室外部检查并录像。 在插入腔室之前，可能将成核剂添加到细丝中。 这些包括不挥发的可溶性颗粒，如硫酸，以及不溶性矿物，陨石和飞机排气材料。 冷的高空云层对太阳和红外辐射的传输，从而对全球气候产生重要影响。 它们也在臭氧的产生和破坏中发挥作用。 尽管它们很重要，但由于在大多数飞机的天花板以上的高度进行现场测量的困难，这些云的物理特性并不为人所知。 该项目的实验室实验将模拟极端大气条件，并提供通过其他手段几乎无法获得的云的微物理特性的必要信息。

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.