|
Cyber Snowflakes
Design
your own snowflake that bears your name online
About
the 3D Snowflake Model Lucky Draw
Results
of the 3D Snowflake Model Lucky Draw
3D
Snowflake Model Lucky Draw Process
Know more about
snowflake
The
conditions of the form of snowflake
Clouds are made
up of water vapour and composed of very tiny water
droplets. In continental clouds, most droplets are
smaller than one of seven hundredth of an inch chay
to S.I. unit 0.04 millimetre in diameter. Many people
believe that when the temperature gets below 0°C,
the water will freeze. However, it is not always
the case. Most scientists believe that the basic
process is like the following.
Normally, water droplets
will not stick with each other, unless there are
some conditions satisfied. First of all, the temperature
of the atmosphere is around the freezing temperature
of water which is 0°C. However, pure water droplets
will not automatically condense in such temperature.
It is because water droplets do not contain a special
kind of particle, which is the second condition,
called a condensation nucleus. Most of the freezing
nuclei are at about -10°C and allow the cloud
droplets to condense around them. In the sky, if
water droplets freeze, they must need something
to stick to. Dust is the material that is the easiest
found in the atmosphere. Smog, or even bacteria,
can act as the freezing nuclei too.
A group of Soviet scientists
did a research and their results and confirmed the
above explanation. They used aircrafts to release
man-made particles made of dust in the sky. Then
they collected and measured the ice nuclei (freezing
nuclei). It showed that in the presence of those
man-made particles, the size of the snow crystal
were considerably bigger than natural one.
The
process of snowflake formation
When the temperature
is below 0°C and in the presence of freezing
nuclei, the water droplets begin to freeze and become
ice crystals. As those water droplets are too tiny
to see, many people mistake this process as sublimation,
by which the water vapour skips the liquid state
and turns directly into ice.
When ice crystals begin to form, water droplets
around those ice crystals will freeze and cling
with them together. As they continue to grow, they
attract more water droplets and expand to form larger
sizes. When they join with around 2 to 200 ice crystals,
they will become unique shape of snowflakes depending
on the condition of the atmosphere.
Snow particles fall at rates ranging from nearly
zero for tiny crystals to about a metre per second
for a typical snowflake and several times larger
for melting snow. When snow crystals strike supercooled
droplets, the droplets will immediately freeze onto
them. This process, called riming, forms soft particles
known as snow pellets or grains. In temperate zones,
the melting of snow pellets provides much of the
rainfall from cumulus clouds.
When ice crystal grows, it attracts more and more
water molecules to form snowflakes. A construction
mystery of snowflakes is the average hexagonal shape,
which may contain as many as 100 million or more
water molecules. In certain conditions, the growing
process proceeds in both perfectly horizontal and
perpendicular directions, thus building a broader
and thicker crystal in hexagonal symmetry. Amazingly,
this symmetry is always maintained out when the
size is increased.
Growth
of Snowflake
When snow forms, the
atmosphere is saturated with water vapour and the
temperature should be below 0°C. Tiny ice crystals
begin to form around the freezing nuclei. Then,
ice crystals join together and snowflakes are formed.
This process is called crystallization. During crystallization,
the water molecules will change from liquid state
to solid state with their most basic alignment.
As the basic form of ice crystals is a hexagonal
prism, most ice crystals are six-sided in shape
at the beginning. When more water molecules join
the ice crystals, they will build up around the
first hexagon and maintain the shape of the crystal
as it grows.
Although most ice crystals are formed in six-sided
symmetry, the crystals can result in many different
shapes which depend mostly on temperature. If the
temperature is lower than -30°C, the ice crystals
will form with hexagonal columns. At around -15°C,
the ice crystals will form with hexagonal plates
which are the typical flat snowflakes we see. When
the temperature is up to around -5°C, needles
shaped crystals and many other undetermined shaped
crystals appear. As the higher the clouds, the lower
the temperature. So in high clouds, six-sided hexagonal
columns are more common. Flat hexagonal plate snowflakes
are formed in the middle clouds while many different
shapes of crystals are formed in the low clouds.
However, the real situation is much more complex
and the whole picture is still not well understood.
Size
of Snowflake
Many people think that
snowflakes are of snow faller from the sky and so
they think that snowflakes are as large as a snowball.
Actually, the term snowflake refers to an individual
snow crystal, while snow falling from the sky are
called snowballs which include hundreds or even
thousands of small snowflakes stuck together. Now,
you can imagine how small snowflakes are.
Snow crystals are typically
between 0.5 to 3 millimetres in diameter whereas
snowflakes are about 10 mm in size. Snowflakes weigh
around 1 gram per 3000 to 10000 snowflakes. Some
large snowflakes may typically be as large as 200
to 400 mm (0.79 to 1.57 inches), but occasionally
some giants may also form. Exceptionally large snowflakes
can exceed 500 mm (2 inches) and contain hundreds
of individual crystals. For a snowflake to grow
to an exceptionally large size, conditions must
be perfect. Besides having ideal temperature for
stickiness, the winds must not too strong or else
the large flakes will break up as they fall.
Snowflakes form when air temperature near the earth's
surface is not far from the freezing point. Snows
crystals adhere to one another better within this
temperature range. At very cold temperatures, snowflakes
are uncommon, and snow comprises mainly snow crystals.
According to a research, when the temperature is
-36°C, the average size of snow crystal is 0.017
square millimetres. At -24°C the average size
is 0.034 square millimetres. At -18°C, the average
sizes is increased to 0.084 square millimetres.
At -6°C the average sizes is 0.256 square millimetres.
At -3°C the average size of snow crystals can
be as big as 0.811 square millimetres.
Six-side
structure of snowflakes
We know that the hexagonal
shape of snow crystals can be classified into two
main types: plate-like and column-like. The beautiful
snowflakes that we usually see have basic plate-like
with 6-side symmetries. They usually form under
temperature between -5°C to - 20°C. The
column-like forms include needles or hollow columns.
Needle shape crystals form between 0°C to -5°C
while hollow column form below -20°C.
 If we
want to understand why most ice crystals are hexagonal
prisms, we should study water molecules first. Water
molecules are made of two hydrogen atoms and one
oxygen atom (that is why we sometimes call water
H2O). They stick together by a strong
bonding called covalent bond.
When water cools to freezing point, the water molecules
collide together to form solid ice crystals. They
form a bond called a hydrogen bond that is strong
enough to stick the two water molecules together.
When molecules stick together, they form the most
stable arrangement. In water molecules, the most
stable arrangement consists of six water molecules
forming a hexagonal shape. That is why most ice
crystals have 6-side symmetry.
When more water molecules from the surroundings
stick to the ice crystals, most of them will stick
to the corners of the hexagonal ice crystal plate.
It is because the corners are easier to attract
water molecules than the edges. So, a snowflake
will always grow from its corners.
Uniqueness
of Snowflakes
Long time ago, a scientist
did a research about snowflakes. He used microscopes
to examine the shape of around 5000 snowflakes.
To his amazement, he found that no two snowflakes
were exactly the same shape. Each snowflake has
its own unique pattern.
Scientists tried to solve the mystery of snowflakes.
They discovered that snowflakes are extremely sensitive
to the change of atmospheric conditions. A small
change in temperature or humidity can bring about
an abrupt change in the growth pattern of snowflakes.
In the atmosphere, the temperature and the humidity
are constantly changing. That is why it is difficult
to find two snow crystals that are exactly alike.
In fact, the sharpness of snowflakes reflects its
growth conditions. For example, when we see a snowflake
with plate-like shape and needles-like arms, we
can guess that when this snowflake was formed, the
temperature was between -5°C and - 20°C
so that a plate-like ball could be generated, and
then the temperature got warm to between 0°C
and -5°C for it to get the needle arms. Also,
the longer the snowflake drifting in the skies,
the more complicated its resulting shape.
|
