AGS-FIRP Track 2: Untangling the physics of aerosol activation, turbulence, and drizzle formation: Pi Chamber experiments and numerical simulation

大气中的云通过对太阳辐射和水循环的影响对天气和气候产生非常大的影响，但由于这些系统的复杂性，它们的形成，寿命和行为的许多方面仍然不清楚。从太空中，人们可以看到大片的云，跨越数百或数千公里，而与此同时，这些云是由液滴和气溶胶组成的，其尺寸小于几十微米。一个单一的亚微米气溶胶的尺度之间的巨大差距，云滴在其上生长，人们可以从太空中看到云街，突出了开发能够准确预测云的关键特性的数值模型的挑战。这个项目的目的是关注这个尺寸范围的小端：不同类型的气溶胶如何导致不同类型的云滴，而背景空气是一种搅动的水分混合物？某些类型的气溶胶，如海盐，比其他类型的更容易凝结水，如矿物粉尘。了解湍流，气溶胶类型/大小和云滴如何相互作用对于代表各种污染条件下的云的增长至关重要，该项目的目标是提供小尺度知识和模型组件，最终将导致更准确的天气和气候预测。该项目有两个互补的组成部分，用于研究与云-气溶胶-湍流相互作用有关的多个问题。第一种是使用能够解析湍流以及大量单个气溶胶和液滴的运动和行为的极高分辨率数值模拟。这种拉格朗日框架属于一类新的云模型，非常适合研究液滴生长及其与湍流耦合的复杂细节。为了补充这些模拟，将在密歇根理工大学的“Pi Chamber”进行相应的实验。该室是一个实验设施，可以创建高度受控的云，可以在多种配置中进行监测和测量-包括多种类型/大小的气溶胶。该实验/数值组合将针对与（1）气溶胶吸湿性，（2）过饱和波动，（3）液滴沉降/沉积和（4）毛毛雨形成有关的问题。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。

Clouds in the atmosphere have a very large effect on weather and climate through effects on solar radiation and the water cycle, and yet many aspects of their formation, lifetime, and behavior remain unclear due to the complexity of these systems. From space, one can see large swaths of clouds spanning hundreds or thousands of kilometers, while at the same time these clouds are composed of droplets and aerosols whose size are less than a few dozen micrometers. This immense gap between the scales of a single, sub-micron aerosol, upon which a cloud droplet grows, to a cloud street that one can see from space, highlights the challenge of developing numerical models that are able to accurately predict the key properties of clouds that govern Earth’s climate and weather. This project is aimed at focusing on the small end of this size spectrum: how do different types of aerosols cause different types of cloud droplets, all while the background air is a churning mixture of moisture? Certain types of aerosols, such as sea salt, act to condense water more easily than others, such as mineral dust. Understanding how turbulence, aerosol type/size, and cloud droplets interact is crucial for representing the growth of clouds in various pollution conditions, and the goals of this project are to provide the small-scale knowledge and model components which will ultimately lead to more accurate weather and climate predictions. The project has two complementary components for studying multiple questions pertaining to cloud-aerosol-turbulence interaction. The first is using extremely high-resolution numerical simulations capable of resolving the turbulent flow, as well as the motion and behavior of large numbers of individual aerosols and droplets. This Lagrangian framework belongs to a new class of cloud models which are ideally suited for studying the intricate details of droplet growth and its coupling with a turbulent flow. To complement these simulations, corresponding experiments at Michigan Technological University’s “Pi Chamber” will be conducted. This chamber is an experimental facility which can create highly controlled clouds that can be monitored and measured in multiple configurations --- including with multiple types/sizes of aerosols. This experimental/numerical combination will target questions related to (1) aerosol hygroscopicity, (2) supersaturation fluctuations, (3) droplet settling/deposition, and (4) drizzle formation.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.