Microphysics Contrasts between Stratus and Cumulus Clouds

该奖项支持云类型和导致水凝结形成云滴的微小颗粒之间的联系的研究。这些微小的粒子也被称为云凝聚核(CCN)。由于许多CCN来自大气污染，其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。但云也会通过云滴内部的化学反应和云滴之间的聚合来改变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。在一个分析数据集中，云处理似乎增强了AIE，但在另一个数据集中，AIE似乎被云处理降低。拟议的研究将把这一分析扩展到在世界不同地区和不同类型云的不同时间段收集的许多其他现有数据集。这项研究可能有助于确定AIE是否显著抵消或加剧了全球气候的温室效应。因此，研究结果可以为国家和国际能源政策提供科学依据。这项基础性研究将增加云处理的知识，改进天气和气候预报，并评估为抵消全球变暖而提出的云增亮地球工程计划。此外，一名研究生将接受培训，并接触到广泛的云场运动数据，以开始他/她的科学生涯。气溶胶大小的双峰分布是由于云滴像往常一样蒸发后，其内部溶解物质增加所致。微量气体的化学反应扩散到云滴中，云处理过程中云滴之间的聚合形成较大的粒子。在较厚的积云中，合并所需的较大液滴更为丰富，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，或者是由于这些云类型之间的云动力学的固有差异。这些相反的云层效应表现在云层亮度和云层寿命方面的差异，这两者都会影响气候。所提出的分析方法是基于详细的高分辨率CCN光谱测量的双峰性/单峰性，并与云滴浓度、平均直径、光谱宽度和细雨量等云特征进行比较。这些云微物理特征将在不同的云液态水含量上进行检验，以确定卷吸对云微物理和CCN模式的竞争作用。根据相关的CCN谱按形态分组的云特征的不同层次的结果应该揭示在不同环境和云类型中云和细雨特征对CCN形态的响应。这可能证实或反驳双峰CCN对层云和积云中AIE的相反影响，并可能从这些云类型之间的垂直风的差异中理清化学或合并处理的影响。这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势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.