This is Steve Ember.
And this is Bob Doughty with SCIENCE IN THE NEWS, a VOA Special
English program about recent developments in science. Today,
we tell you everything you ever wanted to know about snow.
Winter weather is returning to northern areas of the world.
In much of the United States, winter means the return of snow.
Snow is a subject of great interest to weather experts. Experts
sometimes have difficulty estimating where, when or how much
snow will fall. One reason is that heavy amounts of snow fall
in surprisingly small areas. Another reason is that a small
change in temperature can mean the difference between snow and
Snow is a form of frozen water. It contains many groups of tiny
ice particles called snow crystals. These crystals grow from
water particles in cold clouds. They usually grow around a piece
of dust. All snow crystals have six sides, but they grow in
different shapes. The shape depends mainly on the temperature
and water levels in the air.
Snow crystals grow in one of two designs -- platelike and columnar.
Platelike crystals are flat. They form when the air temperature
is about fifteen degrees below zero Celsius. Columnar snow crystals
look like sticks of ice. They form when the temperature is about
five degrees below zero Celsius.
The shape of a snow crystal may change from one form to another
as the crystal passes through levels of air with different temperatures.
When melting snow crystals or raindrops fall through very cold
air, they freeze to form small particles of ice, called sleet.
Groups of frozen water droplets are called snow pellets. Under
some conditions, these particles may grow larger and form solid
pieces of ice, or hail.
(Photo - E. Conan)
When snow crystals stick together, they produce snowflakes.
Snowflakes come in different sizes. As many as one-hundred crystals
may join together to form a snowflake larger than two-and-one-half
centimeters. Under some conditions, snowflakes can form that
are five centimeters long. Usually, this requires near freezing
temperatures, light winds and changing conditions in Earth¡¯s
Snow contains much less water than rain. About fifteen centimeters
of wet snow has as much water as two-and-one-half centimeters
of rain. About seventy-six centimeters of dry snow equals the
water in two-and-one-half centimeters of rain.
Mongolia: Body of a frozen animal.
Much of the water we use comes from snow. Melting snow provides
water for rivers, electric power centers and agricultural crops.
In the western United States, mountain snow provides up to seventy-five
percent of all surface water supplies.
Snowfall helps to protect plants and some wild animals from
cold, winter weather. Fresh snow is made largely of air trapped
among the snow crystals. Because the air has trouble moving,
the movement of heat is greatly reduced.
Snow also is known to influence the movement of sound waves.
When there is fresh snow on the ground, the surface of the snow
takes in, or absorbs, sound waves. However, snow can become
hard and flat as it becomes older or if there have been strong
winds. Then the snow¡¯s surface will help to send
back sound waves. Under these conditions, sounds may seem clearer
and travel farther.
Generally, the color of snow and ice appears white. This is
because the light we see from the sun is white. Most natural
materials take in some sunlight. This gives them their color.
However, when light travels from air to snow, some light is
sent back, or reflected. Snow crystals have many surfaces to
reflect sunlight. Yet the snow does take in a little sunlight.
It is this light that gives snow its white appearance.
Sometimes, snow or ice may appear to be blue. The blue light
is the product of a long travel path through the snow or ice.
In simple terms, think of snow or ice as a filter. A filter
is designed to reject some substances, while permitting others
to pass through. In the case of snow, all the light makes it
through if the snow is only a centimeter thick. If it is a meter
or more thick, however, blue light often can be seen.
(Photo - Steve Ember)
Snow falls in extreme northern and southern areas of the world
throughout the year. However, the heaviest snowfalls have been
reported in the mountains of other areas during winter. These
areas include the Alps in Italy and Switzerland, the coastal
mountains of western Canada, and the Sierra Nevada and Rocky
mountains in the United States. In warmer climates, snow is
known to fall in areas over four-thousand-nine-hundred meters
above sea level.
Each year, the continental United States has an average of
one-hundred snow storms. An average storm produces snow for
two to five days. Almost every part of the country has received
snowfall at one time or another. Even parts of southern Florida
have reported a few snowflakes.
The national record for snowfall in a single season was set
in nineteen-seventy-one and nineteen-seventy-two. Two-thousand-eight-hundred-fifty
centimeters of snow fell at Ranier Paradise Ranger Station in
the northwestern state of Washington.
People in many other areas have little or no snowfall. In nineteen-thirty-six,
a physicist from Japan produced the first man-made snow in a
laboratory. During the nineteen-forties, several American scientists
developed methods for making snow in other areas. Clouds with
extremely cool water are mixed with man-made ice crystals, such
as silver iodide and metaldehyde crystals. Sometimes, dry ice
particles or liquid propane are used. Today, special machines
are used to produce limited amounts of snow for winter holiday
Snow is responsible for the deaths of hundreds of people in
the United States every year. Many people die in traffic accidents
on roads that are covered with snow or ice. Others die from
being out in the cold or from heart attacks caused by extreme
A few years ago, a major storm caused serious problems in the
eastern United States. It struck the Southeast in January, ninety-ninety-six,
before moving up the East Coast. The storm was blamed for more
than one-hundred deaths. It forced nine states to declare emergency
Virginia and West Virginia were hit hardest. In some areas
there, snowfall amounts were more than one-meter high. Several
states limited driving to emergency vehicles. Most major airports
were closed for at least a day or two.
A week later, two other storms brought additional snow to the
East Coast. In the New York City area, the added weight of the
snow forced the tops of some buildings to break down. Many travelers
were forced to walk long distances through deep snow to get
to train stations.
People may not be able to avoid living in areas where it snows
often. However, they can avoid becoming victims of winter snowstorms.
People should stay in their homes until the storm has passed.
While removing large amounts of snow, they should stop and rest
often. Difficult physical activity during snow removal can cause
a heart attack. It is always a good idea to keep a lot of necessary
supplies in the home even before winter begins. These supplies
include food, medicine, clean water, and extra power supplies.
Some drivers have become trapped in their vehicles during a
snowstorm. If this happens, people should remain in or near
their car unless they see some kind of help. They should get
out and clear space around the vehicle to prevent the possibility
of carbon monoxide gas poisoning.
People should tie a bright-colored object to the top of their
car to increase the chance of rescue. Inside the car, they should
open a window a little for fresh air and turn on the engine
for ten or fifteen minutes every hour for heat.
People living in areas where winter storms are likely should
carry emergency supplies in their vehicle. These include food,
emergency medical supplies, and extra clothing to stay warm
and dry. People in these areas should always be prepared for
winter emergencies. Snow can be beautiful to look at, but it
can also be dangerous.
This SCIENCE IN THE NEWS program was written and produced by
Cynthia Kirk. This is Steve Ember.
And this is Bob Doughty. Join us again next week for more news
about science in Special English on the Voice of America.
This Science Report is published courtesy