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

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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.