Laboratory Experiments on Ice Particle Microphysics and Chemistry

该奖项支持有关冰成核、水滴冻结时的变形和破碎、冰晶的光散射特性以及冰晶表面化学的实验室实验。具体项目包括：(1)确定含有盐类的溶液液滴的均匀冻结温度，这被认为是低平流层中发现的典型液滴；(2)确定海冰中发现的细菌的异质成核特性；(3)研究冰滴变形和破碎的条件；(4)测量冰晶的散射相函数，以便与理论计算相比较；(5)测量由不同过程形成的冰表面的酸碱度及其对杂质和微量气体存在的依赖。关于液滴冻结的工作使用了一个冷冻管，在冷冻管中，液滴通过精确控制的温度和湿度通过空气缓慢下降，以接近高大气中的条件。冰晶生长和散射的研究使用了一个带有电动平衡的云室，它允许在温度、压力和湿度的可控条件下，长时间地观察单个悬浮晶体的生长或蒸发过程。这项工作的动机是需要更好地了解卷云的微物理特征-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，云对阳光的影响的实测值和计算值之间存在差异。具有良好特征的尺寸、形状和取向的晶体的光散射的实验室测量将使评估不同的散射模型成为可能。结果还将改进冰晶形成速度的表征，作为液滴温度、大小和化学成分的函数，这将在大规模大气模型中有用。

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.