VOICE ONE:
This is SCIENCE IN THE NEWS in VOA Special English. I'm Steve Ember.
VOICE TWO:
And I'm Barbara Klein. Today, we tell you everything you ever wanted to know
about snow.
(MUSIC)
VOICE ONE:
Winter weather has returned 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 rain.
VOICE TWO:
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.
VOICE ONE:
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.
(MUSIC)
VOICE TWO:
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
atmosphere.
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 76
centimeters of dry snow equals the water in two and one-half centimeters of
rain.
VOICE ONE:
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 75 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.
VOICE TWO:
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.
(MUSIC)
VOICE ONE:
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 4,900 meters above sea level.
VOICE TWO:
Each year, the continental United States has an average of one hundred
snowstorms. 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 1998 and 1999.
2,895 centimeters of snow fell at the Mount Baker Ski area in the northwestern
state of Washington.
VOICE ONE:
People in many other areas have little or no snowfall. In 1936, a physicist
from Japan produced the first man-made snow in a laboratory. During the 1940s,
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 ski areas.
(MUSIC)
VOICE TWO:
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 physical activity.
Several years ago, a major storm caused serious problems in the eastern
United States. It struck the Southeast in January, 1996, before moving up the
East Coast. The storm was blamed for more than 100 deaths. It forced nine
states to declare emergency measures.
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.
VOICE ONE:
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.
VOICE TWO:
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.
(MUSIC)
VOICE ONE:
This SCIENCE IN THE NEWS program was written by George Grow. Our producer was
Brianna Blake. I'm Steve Ember.
VOICE TWO:
And I'm Barbara Klein. Join us again next week for more news about science in
Special English on the Voice of America.
點(diǎn)擊進(jìn)入更多VOA慢速
（來(lái)源:VOA 英語(yǔ)點(diǎn)津姍姍編輯）
