Date of Award


Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Atmospheric Sciences (PhD)

Administrative Home Department

Department of Physics

Advisor 1

Will Cantrell

Committee Member 1

Raymond Shaw

Committee Member 2

Mike Larsen

Committee Member 3

Caroline Jarrold


The saturation ratio determines the growth of cloud droplets by condensation and activation of aerosol particles. In a uniform environment, the interactions between the saturation ratio and cloud droplets are well understood. However, the presence of turbulent mixing causes spatial and temporal variability in the temperature, water vapor and the saturation ratio. When applied to a cloud, the variability in S has been shown to broaden the cloud droplet size distribution through each droplet having its own growth rate and history. When droplets grow by condensation or evaporation, water vapor and heat feedback with the environment, altering the distribution of the saturation ratio.

This dissertation explores the nature of the variability in the saturation ratio in clouds using measurements and simulations of the Michigan Tech Pi chamber. Measurements of the Pi chamber show the Large Scale Circulation contributes to the variability of the saturation ratio. We have found the saturation ratio has significant fluctuations in both moist and cloudy conditions. Increasing the concentration of cloud condensation nuclei was shown to decrease the mean saturation ratio, however the variance was unchanged. Using a box model alongside the high resolution simulation of the Pi chamber, we found fluctuations in the saturation ratio cause aerosol particles to activate in mean subsaturated conditions. We show turbulent fluctuations in the supersaturation increases the concentration of cloud condensation nuclei, by increasing the efficiency of aerosol activation.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.