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

暖云的光学性质取决于液滴的尺寸分布和力矩。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心。本项目将在气溶胶第一和第二间接效应(反照率和寿命效应)的背景下，研究气溶胶和云滴如何在湍流环境中相互作用。研究将在PI小室进行，在该小室中，云是在湍流环境中通过等压混合产生的。实验室环境允许在存在恒定的热力学强迫和湍流特性的情况下气溶胶-云的相互作用。该实验室系统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。该项目的目标是调查云与周围气溶胶种群相互作用和净化时的瞬变响应；研究湍流环境中的过饱和变异性；调查稳态、湍流环境中云滴的增长，特别是了解相松弛时间和湍流相关时间的相对作用；继续开发用于比较和解释实验室观测的大涡模拟(LES)/bin-微物理模式，最终目的是作为通向整个大气背景的桥梁；并对形成和测量混合相云的能力进行初步探索工作。智力优点：PI小室的结果已经导致验证，当相松弛时间与湍流相关时间相比时，云滴凝结增长是根本不同的；并说明这提供了一种加速气溶胶激活和云坍塌的机制。这两个过程从根本上都与气溶胶-云相互作用及其对间接影响的影响有关。这项研究直接建立在这些结果的基础上，并将导致对云对气溶胶的净化、湍流中的过饱和度可变性以及过饱和度可变性如何影响云滴尺寸分布的扩大的更深入的理解，这些都是降水形成问题的关键方面。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发现的现象的链接。最后，这项研究将进一步深入了解产生稳态混合相云的必要条件。更广泛的影响：降水形成和云的辐射特性是气候和天气预报问题的关键方面。因此，它们是直接与社会相关的问题，有可能转化为切实的经济利益和人类状况的改善。PI Chamber使用Rayleigh-Benard对流作为产生云形成的过饱和的机制。这项研究将为研究瑞利-贝纳德对流的不同研究人员做出贡献。它将与该社区研究的广泛应用问题有关，从恒星大气到地幔，再到涉及湍流热传输的无数工程问题的应用。最后，圆周室为教育提供了宝贵的机会：从K-12级别的外展，到本科生实习和高级项目，最后到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。云室实验室的外展活动将继续定期进行。这一奖项反映了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。

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.