Snow Crystals,
Our Friends
James Provencio
Katie Ohsann
Stephen Barta
Dave Gosselin
Introduction
Have you ever wondered
about those little white flakes that fall from the sky in the winter? Those
little white flakes are more than just simple little flakes! Snowflakes
are actually very complex patterns at the microscopic level. In this project
we will refer to snowflakes as snow crystals because it is the elementary
form of which they are made.But before we can call them snow crystals they
first form as ice crystals. The life of an ice crystal is played out in
many ways but there are two common ways. The crystal can fall to the earth
in its original formation, and this really only happens in the insanely
cold regions of the Artic and Antarctic. However, what is even more common
throughout the world is that the ice crystal may grow into a snow crystal.
This happens by sublimation (water vapor turning directly into ice). As
ice crystals fall and join together with other crystals they form what
we know as snow. And with that in mind there are six different basic types
of these snow crystalline patterns, which are the basis for other more
dramatic patterns. Each crystal is formed depending on the atmospheric
conditions present such as the temperature and the amount of water vapor
obtainable in the air. This also determines its forthcoming shape. The
following paragraphs will give a brief description of each.
Introduction Reference Site:
Snow Crystals
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The first pattern
we will look at is a Star Crystal. Star crystals
start to form at temperatures close to -15 degrees C, and are probably
the most common of all snowflakes. They are just as delicate as they look.
There is also what is referred to as a Superstar however; these are very
rare because large snowflakes are broken down by the wind when they fall
to the ground. Either the force of the wind or the collision of other snowflakes
causes this. Also under the right conditions several star crystals can
join together to form a larger snow crystal.
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The second pattern we will
look at is called the Dendrite Star. Essentially
these are three-dimensional star crystals. They have several branches that
grow off it in many directions. These snowflakes are usually formed under
extremely cold conditions, particularly -25 to -20 degrees C. High levels
of atmospheric moisture are also vital.
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The next basic pattern
of snowflakes is referred to as Columns. Columns
have a higher density than star crystals, and are typically smaller. Usually
this pattern is produced when the air is dryer. Columns are produced in
a wide range of temperature, anywhere from -25 to -15 degrees C.
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Plates
are another basic pattern in snowflake structure. They are shapes that
would essentially be stars, but they lack moisture. Basically, a plate
is formed when there is not enough atmospheric water vapor available to
form the delicate arms of a classic star. Plates are usually formed at
temperatures of -20 to -10 degrees C.
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The fifth basic pattern
is a Capped Column. They are formed when the
particle of snow passes through different temperature zones on its way
to the ground. Columns form at higher dryer areas of a cloud, and then
mix/combine with star flakes as they fall through lower and wetter cloud
heights.
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Sixth and lastly there
are Needles. They are formed at the upper
region of the temperature spectrum, usually when ground temperatures are
at or near the freezing point. To be allowed to grow the crystals need
the air temperature to be -10 to -5 degrees C. Needles tend to produce
a dense and stiff snow pack, which unfortunately can produce an avalanche
under the right conditions.
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Snow Crystals Reference Sites:
http://www.its.caltech.edu/~atomic/snowcrystals/http://www.colorado.edu/epob/epob4630estone/EPOB4630/Textfolder/STUDYINGSNOW.html
Formation of Snowflakes
As
mentioned before snowflakes actually start as ice crystals from the sublimation
of water vapor. These ice crystals freeze around tiny solid particles in
the air. These particles could be dust or even salt. As it falls to the
earth it joins with more and more snow crystals to form snowflakes. Snow
crystals can go through different air temperatures, air currents, and humidity
levels as they fall to the earth. The actual shape of a snowflake is determined
on several conditions. These are temperature, wind, time it takes to fall
to the ground, and the amount of water vapor in the air. Changes in anyone
of these conditions can alter the snowflake drastically. What makes a snowflake
six sided is the water molecules in the crystal. Water molecules are attracted
to each other and grow in six directions naturally. This is how Snowflakes
have always had six sides.Formation Reference Sites
Conclusion
Now you may never look
at a snowflake the same again. After reviewing the facts, you may realize
that there's more that meets the eyes to something so taken for granted.
Who would've known there was actually patterns to the elements that create
those extreme winters for some. In fact, there is a world to know about
how snow crystals are formed. For us, the authors, we learned a great deal
about the complex universe of snow. Maybe next time you're in the middle
of a snowstorm, you'll attempt to catch a piece of this world, and determine:
is it a star? ; a dendrite star? ; a column? ; a capped column? ; or a
needle? Just a little something new to ponder.
Early Snow Crystal Observations
Go to: http://www.its.caltech.edu/~atomic/snowcrystals/earlyobs/earlyobs.htm
for
the full story on each early observer.
- 1611 – Johannes Kepler
In 1611 Johannes Kepler published a short treatise
On
the Six-Cornered Snowflake, which is perhaps the first scientific reference
to snow crystals. In his Treatise Kepler ponders the Question of why snow
crystals always exhibit six-fold symmetry.
- 1635 – René Descartes
Philosopher and mathematician
René Descartes was the first to pen a reasonably accurate description
of snow crystal morphologies, about as well as can be done with the naked
eye.
- 1665 – Robert Hooke
In 1665 Robert Hooke published a large volume entitled
Micrographia, containing sketches of practically everything Hooke
could view with the latest invention of the day, the microscope.
- 1931 – Wilson A. Bentley
Wilson Bentley (1865-1931)
was an American farmer and snow crystal photomicrographer, who during his
lifetime captured some 5000 snow crystal images.
- 1954 – Ukichiro Nakaya
Ukichiro Nakaya was
the first person to perform a true systematic study of snow crystals, which
resulted in a giant leap in our understanding of how snow crystals form.
Nakaya's real triumph, however, came from growing artificial snow crystals
in the laboratory under controlled conditions.