Ice Formation Processes in Upper Tropospheric Cloud Conditions

Demott/摘要 这项研究的目的是确定大气气溶胶的化学成分如何影响卷云的形成。 待测试的假设是，通过均匀冷冻成核的冰形成与在低于-35摄氏度的温度下存在于低于100%相对湿度的溶液液滴的理论一致，并且部分可溶的大气气溶胶的不溶性组分在不太严格的条件下容易用作非均质冷冻核。 系统的实验室测量温度冷至-60摄氏度将使用连续流扩散室，以确定开始溶质 在大气相关的硫酸盐气溶胶上形成的溶液液滴中均匀冻结成核的浓度条件。 将对包括充分表征的不溶性气溶胶组分的气溶胶重复测量。 可溶性和部分可溶性气溶胶分布的验证测量将在云室中进行 其模拟绝热空气块上升。 实验室数据将与对流层上部气溶胶和冰核成分的现有数据一起用于对卷云中的冰形成进行数值研究。 预计这些结果将与气溶胶通过控制云的微物理组成而影响对流层上层云的辐射特性的作用有关。

Demott/Abstract The objective of this research are to determine how the chemical composition of atmospheric aerosols influences the formation of cirrus clouds. The Hypotheses to be tested are that ice formation by homogeneous freezing nucleation occurs in agreement with theory for solution droplets existing below 100% relative humidity at temperatures below -35 degrees Celsius, and that the insoluble components of partially- soluble atmospheric aerosols readily serve as heterogeneous freezing nuclei under less stringent conditions. Systematic laboratory measurements to temperatures as cold as -60 degrees Celsius will be made using a continuous flow diffusion chamber to determine the onset solute concentration conditions for homogeneous freezing nucleation in solution droplets formed on sulfate aerosols of atmospheric relevance. Measurements will be repeated for aerosols including well-characterized insoluble aerosol components. Validation measurements for distributions of soluble and partially-soluble aerosols will be made in a cloud chamber which simulates adiabatic air parcel ascent. The laboratory data will be used together with existing data on upper tropospheric aerosol and ice nuclei composition to numerically investigate ice formation in cirrus clouds. The results are expected to be relevant to the role of aerosols in influencing the radiative properties of upper tropospheric clouds through controls on cloud microphysical composition.