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Re: Snowflake symmetry

On Wed, 3 Jun 1998, John Mallinckrodt wrote:

This list needs a new thread so ...

I wonder how many list members have ever thought about why *individual*
snowflakes should be so extremely symmetric at the same time that
*different* snowflakes can be so extremely different.

The Museum of Science in Boston once had an underwater snowflake
generator. (Do they still?) Watching this device in action greatly
improved my intuitive grasp of snowflake growth. Be warned though, since
all of the following is how it "fell together" for me. I haven't checked
out any literature on this, so I don't know if my rambles match the
standard thinking.



I had always wrongly imagined that snowflakes tumble as they grow.
Instead, they lay flat, they keep one side towards their direction of
travel. They maintain a boundary layer on the face towards the "wind",
and only their edges extend out into the tiny "breeze" created by their
falling motion. This gives a good reason for the flat geometry: only
the edges of the falling plates are exposed to moisture-laden air. The
boundary layer on the flat lower faces would already have its moisture
plated out onto the flake.

Sometimes when we fly crosscountry we see the sun's reflection on lakes
hidden below the clouds. But this happens when there are no lakes there
at all! I've been told that this is caused by ice crystals. It makes
sense: Billions of snowflakes, all suspended parallel to the ground, act
like a single gigantic mirror many miles across. I hope that there are no
natural processes which could ever distort the shape of these mirrors.
Hate to fly through the focus of a naturally-occurring "solar furnace"
made of suspended snowflakes.

((((((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))))
William J. Beaty SCIENCE HOBBYIST website
billb@eskimo.com www.eskimo.com/~billb
EE/programmer/sci-exhibits science projects, tesla, weird science
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