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Not Just Flaky Research

Photonics Spectra
Feb 2007
Sally B. Patterson

The commonly held belief that no two snowflakes are alike may be true in the latter stages of the crystals’ development, but at their early stages, the hexagonal prisms are similar. Jon Nelson, a researcher at Sci-cubed, a not-for-profit research organization in North Bend, Wash., and a lecturer at Ritsumeikan University in Kyoto, Japan, has been studying the growth habits of snowflakes for many years.

SnowFlake_TakaDendrite.jpgHe and his colleagues collect fresh snowflakes for observation under a light microscope. He said that others also have tried using scanning-electron microscopes, but that the preparation process destroys some detail. “The images from light microscopes have the advantage that we can see details throughout the crystal,” he said. “This is not possible with the SEM images.”

He explained that the tiny ice crystals start as water droplets condensing on particles of dust. The H2O molecules bond in a characteristic six-sided network. Faster growth at the corners makes branches sprout, and these elongate, become rounded at the tips or sprout side branches. Subtle changes in water vapor and temperature as the flakes fall account for their unique shapes by the time they hit the ground.

Nelson said it is important to learn why the crystals change growth patterns from a needle-habit to a star-shape regime so rapidly. “I know of no other crystals, certainly no common crystals, that have several habit changes over such a small temperature interval, and the magnitude of the change is unprecedented.”

He said that studying snow could help us understand ozone depletion and global warming and how snow crystals — and atmospheric ice in general — affect climate. “The effect of cirrus clouds, which are mostly ice crystals, on climate is poorly understood. One of the major uncertainties is how fast the crystals grow.”

He is working on a crystal growth apparatus, and he wants to explore the electrical charges that snow crystals exchange when they bump against other ice surfaces. These could contribute to the charging of thunderstorms, and understanding them could help us learn how storms produce lightning.

And, come to think of it, why no two lightning bolts are identical.


GLOSSARY
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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