Laboratory Experiments on Ice Particle Microphysics and Chemistry

该奖项支持冰成核、液滴冻结时的扭曲和破碎、冰晶的光散射特性以及冰晶表面的化学性质的实验室实验。具体项目包括：（1）确定含有硫酸铵等盐类的溶液液滴的均匀冻结温度，这被认为是平流层下部液滴的典型特征;（2）确定海冰中细菌的异质成核特性;（3）研究冻结液滴变形和破碎的条件;（4）测量冰晶的散射相函数以与理论计算进行比较：（5）测量由不同过程形成的冰的表面pH值及其对杂质和痕量气体存在的依赖性。液滴冷冻的工作采用冷冻管，液滴在精确控制温度和湿度的空气中缓慢下降，以接近高层大气的条件。冰晶生长和散射的研究采用了一个带有电动天平的云室，可以在温度、压力和湿度的受控条件下长时间观察单个悬浮晶体的生长或蒸发。这项工作的动机是需要更好地了解卷云的微物理特性-它们如何形成，生长和影响太阳辐射的传输。目前，使用不同的辐射传输模型，云对阳光的测量和计算效果之间存在差异。具有良好表征的尺寸、形状和取向的晶体的光散射的实验室测量将使得能够评估不同的散射模型。结果还将提供一个改进的表征率冰晶形成，作为液滴温度，大小和化学成分的函数，这将是有用的大规模大气模型。

This award supports laboratory experiments on ice nucleation, the distortion and shattering of droplets as they freeze, the light-scattering properties of ice crystals, and the chemistry of the ice-crystal surface. Specific projects include (1) determining the homogeneous freezing temperatures of solution droplets containing salts such as ammonium sulfate, thought to be typical of the droplets found in the lower stratosphere; (2) determining the heterogeneous nucleation properties of bacteria found in sea ice; (3) examining the conditions under which freezing drops become deformed and shatter; (4) measuring the scattering phase functions of ice crystals for comparison with theoretical calculations; (5) measuring the pH at the surface of ice formed by different processes and its dependence on the presence of impurities and trace gases. The work on droplet freezing employs a freezing-tube, in which the droplet slowly descends through air with accurately controlled temperature and humidity to approximate conditions in the high atmosphere. The studies of ice crystal growth and scattering employ a cloud chamber with an electrodynamic balance that permits the observation of individual, levitated crystals for long periods of time as they grow or evaporate in controlled conditions of temperature, pressure, and humidity. The work is motivated by the need for a better understanding of the microphysical characteristics of cirrus clouds - how they form, grow, and affect the transfer of solar radiation. Discrepancies currently exist between the measured and computed effects of clouds on sunlight, using different radiative-transfer models. The laboratory measurements of light scattering by crystals with well characterized sizes, shapes, and orientations will enable evaluation of the different scattering models. Results will also provide an improved characterization of the rate at which ice crystals form, as a function of droplet temperature, size, and chemical composition, which will be useful in large-scale atmospheric models.