Laboratory Studies of the Effect of Turbulence on Aerosol-Cloud Interactions

暖云的光学特性取决于云滴的尺度分布及其矩。反过来，它们又受到气溶胶粒子的影响，气溶胶粒子充当云滴形成的核。该项目将研究气溶胶和云滴在湍流环境中如何相互作用，以及气溶胶的第一和第二间接效应（气溶胶效应和寿命效应）。研究将在Pi室中进行，其中云是通过湍流环境中的等压混合产生的。实验室环境允许气溶胶-云相互作用的存在下，恒定的热力学强迫和湍流特性。该实验室系统并不试图重建大气的全部复杂性，而是旨在分离气溶胶-云系统的特定方面，该项目的目标是研究云与周围气溶胶群体相互作用和净化时的瞬态响应;研究湍流环境中的过饱和变化;研究稳定状态湍流环境中云滴的增长，特别是了解相位弛豫时间和湍流相关时间的相对作用;继续开发一个大涡模拟/箱形微物理模型，以便与实验室观测结果进行比较和解释，最终目的是作为通向整个大气环境的桥梁;智力上的优点：从Pi室的结果已经导致了验证，当相弛豫时间与湍流相关时间相比是小的或大的时，通过凝结的云滴增长是根本不同的;并且说明这提供了加速气溶胶激活和云崩溃的机制。这两个过程从根本上都与气溶胶-云的相互作用及其对间接效应的影响有关。这项研究直接建立在这些结果的基础上，将导致对云的气溶胶净化，湍流中的过饱和变化以及过饱和变化如何影响云滴尺寸分布的扩大，降水形成问题的关键方面有更深入的了解。结果还将与LES/bin微物理云模型进行比较，该模型可以作为在更复杂的大气背景下研究实验室中确定的现象的链接。最后，这项研究将提供进一步深入了解的必要条件，以产生稳定状态的混合相cloud.Broader影响：降水的形成和云的辐射特性的气候和天气预报问题的关键方面。因此，它们是直接的社会相关问题，并有可能转化为有形的经济效益和人类条件的改善。Pi室使用瑞利-贝纳德对流作为产生云形成过饱和的机制。这项研究将有助于研究Rayleigh-Benard对流的各种研究人员。它将与该社区研究的广泛应用问题相关，从恒星大气到地幔，再到涉及湍流传热的无数工程问题的应用。最后，Pi Chamber提供了宝贵的教育机会：从K-12水平的推广，到本科生实习和高级项目，最后是研究生和博士后研究。目前的项目包括支持两名全日制研究生，他们将精通云室的操作以及各种相关仪器。 该奖项反映了NSF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。

The optical properties of warm clouds depend on the droplet size distribution and its moments. In turn, these are influenced by the aerosol particles that act as nuclei for the formation of cloud droplets. This project will investigate on how the aerosols and cloud droplets interact within a turbulent environment, in the context of both the aerosol first and second indirect effects (albedo and lifetime effects).The studies will be performed in the Pi Chamber, in which clouds are generated through isobaric mixing within a turbulent environment. The laboratory environment allows for aerosol-cloud interaction in the presence of constant thermodynamic forcing and turbulence properties. The laboratory system does not attempt to reconstruct the full complexity of the atmosphere, but rather aims to isolate specific aspects of the aerosol-cloud system.Objectives of the project are to investigate the transient response of clouds as they interact with and cleanse the surrounding aerosol population; To investigate supersaturation variability in a turbulent environment; To investigate the growth of cloud droplets in a steady-state, turbulent environment, specifically to understand the relative roles of the phase relaxation time and the turbulence correlation times; To continue development of a Large Eddy Simulation (LES)/bin-microphysics model for comparison with and interpretation of laboratory observations, with the eventual purpose of serving as a bridge to the full atmospheric context; And to perform initial exploratory work on the ability to form and measure mixed-phase clouds.Intellectual Merit:Results from the Pi Chamber have already led to the verification that cloud droplet growth by condensation is fundamentally different when the phase relaxation time is small or large compared to the turbulence correlation time; and to the illustration that this provides a mechanism for accelerating aerosol activation and cloud collapse. Both of these processes are fundamentally linked to aerosol-cloud interactions and their influence on indirect effects. This research builds directly on those results and will lead to a deeper understanding of cloud cleansing of aerosols, supersaturation variability in turbulent flows, and how that supersaturation variability influences the broadening of cloud droplet size distributions, key aspects of the precipitation formation problem. The results also will be compared with a LES/bin microphysics cloud model that can serve as a link to studying the phenomena identified in the laboratory in the context of the more complex atmosphere. Finally, the study will provide further insight into the conditions necessary to generate steady-state mixed-phase clouds.Broader Impacts:Precipitation formation and radiative properties of clouds are critical aspects of the climate and weather forecasting problems. They are therefore issues of immediate societal relevance and have potential to translate to tangible economic benefits and improvements in the human condition.The Pi Chamber uses Rayleigh-Benard convection as the mechanism for producing supersaturation for cloud formation. The research will contribute to the diverse community of researchers studying Rayleigh-Benard convection. It will have relevance to the vast range of applied problems studied by that community, from stellar atmospheres to the earth's mantle to applications of myriad engineering problems involving turbulent heat transfer.Finally, the Pi Chamber provides valuable opportunities for education: from outreach at the K-12 levels, to undergraduate internships and senior projects, and finally to graduate student and postdoctoral research. The current project includes support for two full-time graduate students who will become well versed in the operation of the cloud chamber as well as with the wide range of associated instrumentation. Outreach events in the cloud chamber lab will be continued on a regular basis.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.