Using laboratory measurements of vapor-grown ice crystals to infer surface kinetics and estimate deposition coefficients

Open Access
- Author:
- Pokrifka, Gwenore Flora
- Graduate Program:
- Meteorology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 15, 2018
- Committee Members:
- Jerry Y Harrington, Thesis Advisor/Co-Advisor
- Keywords:
- deposition coefficient
surface transitions
ice crystals
surface kinetics
vapor growth
laboratory - Abstract:
- The vapor growth of ice crystals has long been misrepresented in cloud and climate models. Ice crystals growing from water vapor are limited by both the diffusion of vapor to the particle and the kinetics of surface attachment, the latter of which model parameterizations typically ignore. Model parameterizations’ incompleteness is in part due to an incomplete understanding of surface attachment kinetics, which are often represented by a growth efficiency known as the deposition coefficient. This work seeks to improve understanding of the deposition coefficient by studying mass growth from vapor of ten ice particles formed from frozen pure water in a levitation diffusion chamber at temperatures between -43.4 and -40.2 °C. The data are analyzed using a diffusion-kinetics model to predict the particles’ deposition coefficients, and it is found that the model cannot replicate some of the growth rates in the data timeseries. Thus, two new analysis methods are developed to eliminate the deposition coefficient’s dependence on the ice supersaturation, which is uncertain. Estimates of the deposition coefficients using the new analysis methods for five ice particles are in the range of 0.018 – 0.066, 0.008 – 0.02, 0.001, 0.048 – 0.5, and 0.006 – 0.014. These particles can be modeled by a classical, faceted growth method. The remaining ice particles demonstrate growth features linked to ice crystal surface transitions. These particles’ growth timeseries cannot be modeled with a classical growth method, instead requiring variable growth mechanisms in time. Surface transitions cause the deposition coefficient to change rapidly, and they may be responsible for discrepancies in past deposition coefficient measurements.