The Branching Process of Snow Crystals
School: Down to Earth School
Area of Science: physics/mathematics
Interim: What affects the snow flake dendrites’ complexity and how? We believe that the atmospheric temperature and supersaturation (humidity and pressure) and also the rate diffusion of water vapor molecules through the air affects the complexity. We found that snow crystal dendrites form by deposition (from a gaseous state directly into a solid). The longer the water vapor molecules have to depose the slower they travel. The water molecules in a gaseous state, or vapor, freeze onto a nucleus (of dust or pollen). The nucleus may be flat; this causes the molecules of water vapor to freeze uniformly flat on the surface of the nucleus. This process of formation is called faceting. The other formation type is called branching. Branching is when the nucleus, either has a bump or something else creates a bump on the surface, and the water vapor molecules freeze onto this bump making the bump taller or larger. The closer the dendrite tip is to the water molecules the less they have to depose, thus making the process progressively faster. The bump or soon to be branch of the dendrite may also form a second bump which the water molecules may also land on and freeze onto, thus making another branch to the complex branching system.
We plan to build an agent-based computational model (using Netlogo) that shows the dendrites forming and changing. The agents, representing water vapor molecules will diffuse, and get slower as they approach the nucleus, and freeze onto it. We haven’t decided yet, but we may have two sliders, one to control the atmospheric temperature and the other to adjust the supersaturation around the snow crystal dendrite. The model will show the snow crystal branching, so the nucleus will have a bump and the molecules will freeze onto the bump(s). The bump(s) will grow, because of the water molecules freezing onto it and the process will progressively get faster because the bump is growing.
We have emailed two scientists; one whose name is Kenneth G. Libbrecht from California Tech. and the other is from University of Wisconsin, his name is David Griffeath. We have not heard back from either of them yet. We received an email from Ms. Patty Meyer who read our proposal and she ask us a couple of questions and told us a few also that maybe we should try to answer with our model. We also each made rock candy to observe the process of crystallization.
We expect to create a realistic model of snow crystal branching using an agent based language. We hope to eventually make the model also show faceting of the snow crystals. We want the “turtles” (agents) to move/diffuse from the top of the screen and attach and freeze onto the turtle, which is representing the dust, in the center. We also want the nucleus have a small bump and we want the water vapor molecules attach onto the bump and create the branches. Then we will have the branches grow side branches and so on. We may possibly have two sliders one that controls the temperature and the other adjusting supersaturation.
- Libbrecht, Kenneth. February 1, 1999. SnowCrystals.com. November 13, 2012. www.its.caltech.edu/~atomic/snowcrystals/dendrites/dendrite.htm
- Libbrecht, Kenneth. February 1, 1999. SnowCrystals.com. October 18, 2012. www.its.caltech.edu/~atomic/snowcrystals/alike/alike.htm
- 2003 – 2012. Wisegeek.com. October 13,2012.
- Libbrecht, Kenneth. February 1, 1999. SnowCrystals.com. October 26, 2012. http://www.its.caltech.edu/~atomic/snowcrystals/myths/myths.htm
- Libbrecht, Kenneth. February 1, 1999. SnowCrystals.com. October 21, 2012.
Sponsoring Teacher: Maia Chaney
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