Date of Award
Open Access Dissertation
Doctor of Philosophy in Atmospheric Sciences (PhD)
Administrative Home Department
Department of Physics
Committee Member 1
Committee Member 2
Committee Member 3
In this study, we attempt to perform in-cloud measurements, both in the laboratory using the Michigan Tech $\Pi$-chamber and in the atmosphere via the CSET field campaign. Atmospheric turbulence is believed to play a critical role in the growth, development and dissipation of clouds and it is important to study its effect in order to better understand and predict cloud properties such as albedo and lifetime. We use digital in-line holography to measure the effect of turbulence on cloud microphysical properties such as variations in droplet number concentration and droplet or ice particle size. In the first half, we study warm clouds and investigate how cloud droplets grow between the regimes dominated by diffusional growth and growth by collision-coalescence. We propose that microphysical variability in droplet number concentration will lead to local increase in supersaturation fluctuations. Prior stochastic condensation theory assumed constant cloud properties such as phase relaxation time. We create a steady state warm turbulent mixing cloud in the laboratory and use digital in-line holography to obtain local instantaneous droplet number concentrations. We show using these measurements that phase relaxation time distributions are considerably broad leading to additional increase in droplet spectral width. We then compare these results with in-situ measurements of marine stratocumulus clouds during the CSET campaign. We find certain signatures which we define as microphysical fingerprints of stochastic condensation occurring in these clouds. In the second half, we focus our attention on mixed phase clouds which are ubiquitous in the atmosphere but very difficult to measure. By creating steady state mixed phase clouds in the laboratory, using digital in-line holography, we were able to measure cloud droplet and ice particle properties for extended period of time. We show that cloud glaciation is a function of the steady state supersaturation and can be altered by varying the ratio between ice nuclei and cloud condensation nuclei. By varying this ratio, we were able to generate steady state mixed phase clouds with varying ice fraction and study their properties.
Desai, Neel, "Investigation of microphysical properties of laboratory and atmospheric clouds using digital in-line holography", Open Access Dissertation, Michigan Technological University, 2018.
Available for download on Sunday, June 30, 2019