Microphysics Contrasts between Stratus and Cumulus Clouds

该奖项支持对云类型和导致水凝结形成云滴的微小颗粒之间联系的研究。这些微小的粒子也被称为云凝结核（CCN）。由于许多CCN来自空气污染，它们对云的影响，通常被认为是气溶胶间接效应（AIE），造成了最大的气候不确定性。CCN的影响决定了到达地球表面的太阳辐射量。这在很大程度上控制着全球气候。但云也通过云滴内部的化学反应和云滴之间的聚并来改变CCN。这些云过程对CCN的影响反过来又进一步影响控制全球气候的云特性。在一个分析的数据集中，云处理似乎增强了AIE，但在另一个数据集中，云处理似乎降低了AIE。拟议的研究将把这种分析扩展到许多其他现有的数据集，这些数据集在世界不同地区、不同时期、不同类型的云层中收集。这项研究可以帮助确定AIE是否明显抵消或加剧了全球气候的温室效应。因此，该结果可为国家和国际能源政策提供科学依据。这项基础研究将增加对云处理的了解，并导致改善天气和气候预报，以及评估为抵消全球变暖而提出的云层增亮地球工程方案。此外，研究生将接受培训，并接触到广泛的云场运动数据，以开始他/她的科学生涯。双峰气溶胶大小分布是由于云滴蒸发后溶解物质的增加造成的。微量气体的化学反应扩散到云滴中，云滴之间的聚并形成较大的颗粒。在较厚的积云中，聚并所需的较大液滴更丰富，而层云的寿命较长，有利于化学云的处理。双峰气溶胶对积云和层云的相反影响可能是由于这些不同类型的云处理或这些云类型之间云动力学的固有差异。这些相反的云效应表现在影响气候的云亮度和云寿命的差异上。本文提出的分析方法基于详细的高分辨率CCN光谱测量数据的双峰/单峰特征，并与云特征（如液滴浓度、平均直径、光谱宽度和毛毛雨量）进行比较。这些云微物理特征将在不同的云液态水含量上进行检验，以确定夹带对云微物理和CCN模态的竞争作用。根据相关CCN频谱按模态分组的云特征的不同层次的结果应该揭示云和细雨特征如何响应CCN模态在不同的环境和云类型。这可以证实或反驳双峰CCN对层云和积云AIE的相反影响，并可以从这些云类型之间垂直风的差异中解开化学或聚并过程的缠结效应。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award supports research into connections between cloud types and the tiny particles that cause water to condense to form cloud droplets. Those tiny particles are also called cloud condensation nuclei (CCN). Since many CCN come from air pollution, their effects on clouds, which is commonly considered as the aerosol indirect effect (AIE), cause the largest climate uncertainty. Effects of CCN determine the amount of solar radiation that reaches the Earth’s surface. This largely controls global climate. But clouds also change CCN by chemical reactions within cloud droplets and coalescence among cloud droplets. These cloud process effects on CCN in turn further impact the cloud properties that control global climate. In one analyzed data set cloud processing seemed to enhance AIE but in another dataset AIE seemed to be reduced by cloud processing. The proposed research will extend this analysis to many other existing data sets collected in different parts of the world and at various time periods in various types of clouds. This research could help determine whether AIE is appreciably offsetting or enhancing greenhouse warming of the global climate. Thus the result could provide the scientific basis for national and international energy policies. This fundamental research would increase knowledge of cloud processing and lead to improved weather and climate forecasts as well as evaluate cloud brightening geoengineering schemes proposed to offset global warming. In addition, a graduate student will be trained and exposed to a wide array of cloud field campaign data to start his/her scientific career. Bimodal aerosol size distributions are due to increased dissolved material within cloud droplets after they evaporate as they usually do. The chemical reactions by trace gases diffused into cloud droplets and coalescence among cloud droplets from cloud processing form the larger particle. The required larger droplets for coalescence are more abundant in thicker cumulus clouds whereas the longer lifetimes of stratus clouds favor chemical cloud processing. The opposite effects of bimodal aerosol on cumulus and stratus clouds may be due to these different types of cloud processing or to inherent differences in cloud dynamics between these cloud types. These opposite cloud effects are manifested in differences in cloud brightness and cloud lifetime both of which impact climate. The proposed analysis method is based on bimodality/unimodality of detailed high resolution CCN spectral measurements compared with cloud characteristics such as droplet concentration, mean diameter, spectral width, and drizzle amounts. These cloud microphysics characteristics will be examined over various cloud liquid water contents to determine the competing role of entrainment on cloud microphysics and CCN modality. Results of different hierarchies of cloud characteristics according to associated CCN spectra grouped according to modality should reveal how cloud and drizzle characteristics respond to CCN modality in various environments and cloud types. This could confirm or refute opposite impacts of bimodal CCN on AIE in stratus and cumulus clouds and could untangle effects of chemical or coalescence processing from differences in vertical winds between these cloud types.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.