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Aerosol-turbulence-droplet interactions in clouds

Pi chamber logo

Project title

Untangling the physics of aerosol activation, turbulence, and drizzle formation: Pi Chamber experiments and numerical simulation

Sponsor

National Science Foundation AGS-2227012

Project duration

2022-2026

Summary

This project aims to better understand the physics of cloud droplet transport and aerosol activation, from a combined use of turbulence-resolving simulations and experimental observation. In particular, it proposes to leverage the wealth of knowledge gained thus far from Michigan Technical University’s Pi Convection-Cloud Chamber, and expand its impact on the cloud physics community by complementing experimental insight with detailed, Lagrangian-based numerical simulations. It is well-acknowledged that improvements are needed in modeling aerosol activation and droplet size distribution (DSD) evolution, given the importance of these microphysical details on macroscale cloud and precipitation properties. In particular, ongoing research in the Pi Chamber has clearly demonstrated the key role of turbulence and the corresponding fluctuations of supersaturation, whose influence is often neglected in simple models. This deeper understanding of droplet-turbulence interaction, in turn, has informed stochastic models whose ultimate goal is to accurately account for aerosol and droplet microphysics from a Lagrangian point of view as they traverse an unsteady environment, subject to multiple types and scales of physical processes (gravitational settling, collision/coalescence, condensational growth, turbulent fluctuations, etc.).

Complementing the physical experiments attainable in the Pi Chamber with numerical simulations is critical for better understanding the full aerosol-droplet-turbulence interaction relevant not only to the experiments, but to atmospheric clouds. The research centers on four fundamental questions pertaining to: (1) the relative importance of aerosol hygroscopicity and size, particularly in a fluctuating, turbulent environment; (2) the disentangling of the influence of supersaturation fluctuations as distinct turbulence strength, since changes to turbulence kinetic energy will have different influences than purely from changes to thermodynamic forcing; (3) in the Pi Chamber specifically, but also in clouds more generally, the physics dictating the droplet settling/deposition rates and their lifetimes, since this governs exposure to environmental conditions and is one of the key ingredients for stochastic model development; (4) a detailed investigation of the onset of drizzle formation in the context of a fluctuating supersaturation field, especially as it pertains to the conditions which will enhance or even permit this behavior in a laboratory setting. The overall approach is based on a thorough, detailed analysis of a suite of high-resolution simulations aimed at key aspects of cloud droplet activation and cloud-aerosol activation, complemented with corresponding experiments for certain measurable processes.

Experiments being conducted in the pi convection cloud chamber lab
Experiments being conducted in the Pi convection cloud chamber lab at MTU

Publications and presentations

Publications

  1. Gali, K.F., Sadi, H.F., Anderson, J., Beeler, P., Wang, A., Richter, D.H., Shaw, R., Yang, F., Cantrell, W., Fierce, L., 2025, "Aerosol-driven variability of cloud microphysical properties in a turbulent environment", Proceedings of the National Academy of Sciences, Under review
  2. Swartz-Schult, K., Richter, D.H., Grace, A., Bragg, A., Anderson, J., Cantrell, W., Sadi, H.F., Shaw, R., Sulaiman S.V., Grosz, R., 2026, Observed deviation from Stokes' Law in the dry deposition of heavy particles in Rayleigh–Bénard turbulence, Aerosol Science and Technology, 60, 840–857
  3. Chen, S., Krueger, S.K., Dziekan, P., MacMillan, T., Richter, D.H., Schmalfuß, S., Shima, S., Yang, F., Anderson, J., Shaw, R., Cantrell, W., A model intercomparison study of aerosol-cloud-turbulence interactions in a cloud chamber. Part 1: Model results, Journal of Advances in Modeling Earth Systems, 17, e2024MS004562 -- EOS EDITOR'S HIGHLIGHT
  4. Denzel, C. J., A. D. Bragg, D. H. Richter, 2023, "Stochastic model for the residence time of solid particles in turbulent Rayleigh-Bénard flow", Physical Review Fluids, 8(2), 024307
  5. MacMillan, T., Shaw, R., Cantrell, W.H., Richter, D.H., 2022, "Direct numerical simulation of turbulence and microphysics in the Pi Chamber", Physical Review Fluids, 7, 020501

Presentations

  1. Gali, K.F., H. Fahandezh Sadi, J.C. Anderson, P.A. Beeler, A. Wang, D.H. Richter, R.A. Shaw, F. Yang, W. Cantrell, and L.M. Fierce, “The effect of aerosol properties on cloud droplet activation and optical properties in a convective cloud chamber”, presentation at the American Meteorological Society Conference on Cloud Physics, Madison, WI, August 6, 2026
  2. Swartz-Schult, K.J., J.C. Anderson, W. Cantrell, H. Fahandezh Sadi, R.A. Shaw, D.H. Richter, K. Flore Gali, J. Simmons, and S.P. Singh, “Probing kappa-Köhler equivalence in the Pi convection-cloud chamber”, presentation at the American Meteorological Society Conference on Cloud Physics, Madison, WI, August 5, 2026
  3. Fierce, L., Gali, K.F., Cantrell, W., Sadi, H.F., Anderson, J., Beeler, P., Richter, D.H., Shaw, R.A., Wang, A., and Yang, F, “Regime controls on aerosol effects in turbulent clouds: From chamber observations to reduced models of aerosol-cloud interactions”, poster presentation at the 2026 Joint Atmospheric Radiation Measurement (ARM) User Facility/ Atmospheric System Research (ASR) PI Meeting, held virtually July 21-23, 2026
  4. Swartz-Schult, K. J., Richter, D. H., Grace, A., Bragg, A. D., Anderson, J. C., Cantrell, W., Grosz, R., Fahandezh Sadi, H., Shaw, R. A., Sulaiman, S. V., “Exploring removal mechanisms in the Pi Convection–Cloud Chamber”, poster presentation at the American Meteorological Society Annual Meeting, Houston, TX, January 28, 2026. This presentation won 1st place for best student poster presentation
  5. Swartz-Schult, K. J., Anderson, J. C., Cantrell, W., Flore Gali, K., Fahandezh Sadi, H., Shaw, R. A., Simmons, J., Singh, S. P., Richter, D. H., “Probing kappa-Köhler equivalence in the Pi Convection–Cloud Chamber”, presentation at the American Meteorological Society Annual Meeting, Houston, TX, January 28, 2026. This presentation won 3rd place for best student oral presentation
  6. Krueger, S. K., Daniels, G., Bois, C., Anderson, J. C., Shaw, R. A., Chandrakar, K. K., Richter, D. H., Swartz-Schult, K. J., “Estimating mean supersaturation in a convective cloud chamber”, presentation at the American Meteorological Society Annual Meeting, Houston, TX, January 28, 2026
  7. Swartz-Schult, K. J., Richter, D. H., Grace, A., Bragg, A. D., Anderson, J. C., Cantrell, W., Grosz, R., Fahandezh Sadi, H., Shaw, R. A., Sulaiman, S. V., “Exploring removal mechanisms in the Pi Convection–Cloud Chamber”, poster presentation at the American Meteorological Society Annual Meeting, Houston, TX, January 28, 2026
  8. Swartz-Schult, K. J., Anderson, J. C., Cantrell, W., Flore Gali, K., Fahandezh Sadi, H., Shaw, R. A., Simmons, J., Singh, S. P., Richter, D. H., “Probing kappa-Köhler equivalence in the Pi Convection–Cloud Chamber”, presentation at the American Meteorological Society Annual Meeting, Houston, TX, January 28, 2026
  9. Daniels, G., Krueger, S., Bois, C., Shaw, R., Anderson, J., Chandrakar, K., Richter, D.H., Swartz-Shult, K., “Retrieving supersaturation in a convective cloud chamber through droplet size distribution”, presentation at the American Physical Society Division of Fluid Dynamics Meeting, Houston, TX, November 24, 2025
  10. Swartz-Schult, K.J., Richter, D.H., Shaw, R.A., Cantrell, W., Anderson, J.C., Fahandezh Sadi, H., Sulaiman, S.V., Grace, A., "Exploring aerosol removal mechanisms in the Pi cloud chamber," presentation at the American Meteorological Society Annual Meeting, New Orleans, LA, January 15, 2025
  11. Krueger, S., Daniels, G., Anderson, J., Chandrakar, K., Rajagopal, M., Richter, D.H., Shaw, R.A., Swartz-Schult, K.J., "Estimating mean supersaturation in a laboratory convection cloud chamber," poster presentation at the American Meteorological Society Annual Meeting, New Orleans, LA, January 14, 2025
  12. Swartz-Schult, K., Shaw, R., Cantrell, W., Anderson, J., Fahandezh Sadi, H., Sulaiman, S., Grace, A., Richter, D.H., “The settling rates of particles in Rayleigh-Bénard turbulence”, poster presentation at the International Conference on Clouds and Precipitation, Jeju Island, South Korea, July 15, 2024
  13. Swartz-Schult, K., Anderson, J., Sadi, H., Sulaiman, S., Cantrell, W., Shaw, R., Richter, D.H., “The settling rates of particles in Rayleigh-Bénard turbulence”, presentation at the American Physical Society Division of Fluid Dynamics Meeting, Washington, D.C., November 20, 2023
  14. Denzel, C., Bragg, A., and Richter, D.H., “Evolution of superdroplets and their lifetimes in the turbulent Rayleigh Bénard flow of the Pi Chamber”, presentation at the American Meteorological Society Annual Meeting, Denver, CO, January 9, 2023
  15. Denzel, C., Richter, D.H., and Bragg, A., “Physics informed stochastic model for the residence of solid particles in turbulent Rayleigh-Bénard flow”, presentation at the American Physical Society Division of Fluid Dynamics annual meeting, Indianapolis, IN, November 20, 2022
  16. Denzel, C., Bragg, A., and Richter, D.H., “Droplet and aerosol lifetimes in the turbulent Rayleigh-Bénard flow of the Pi Chamber”, poster presentation at the American Meteorological Society 16th Conference on Cloud Physics, Madison, WI, August 9, 2022
  17. Krueger, S., Chen, S., Dziekan, P., MacMillan, T., Richter, D.H., Schmalfuß, S., Shima, S., Yang, F., Shaw, R.A., Cantrell, W., “Intercomparison of model simulations of cloudy Rayleigh-Bénard convection in a laboratory chamber”, oral presentation at the American Physical Society Division of Fluid Dynamics annual meeting, Phoenix, AZ, November 22, 2021
  18. MacMillan, T. & Richter, D.H., “Evaluating cloud droplet spectrum broadening with an analysis of coherent structures in Rayleigh-Benard convection”, oral presentation at the International Conference on Clouds and Precipitation, held virtually on August 6, 2021
  19. MacMillan, T. & Richter, D.H., “Pi chamber DNS overview”, oral presentation at the International Cloud Modeling Workshop, held virtually on July 26, 2021