下雪了，看看 voa 对雪的介绍: About the Snow

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From : http://www.listeningexpress.net/　　
  
SCIENCE IN THE NEWS - Snow
By George Grow
  
Broadcast: December 10, 2002
  
VOICE ONE:
  
This is Steve Ember.
  
VOICE TWO:
  
  
United States
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.
  
(THEME)
  
VOICE ONE:
  
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 rain.
  
VOICE TWO:
  
  
South Africa
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
.
  
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
.
  
  
Russia
(Photo - E. Conan)
(MUSIC BRIDGE)
  
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
seventy-six centimeters of dry snow equals the water in two-and-one-half
centimeters of rain.
  
VOICE ONE:
  
  
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.
  
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 BRIDGE)
  
VOICE ONE:
  
  
Alps
(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.
  
VOICE TWO:
  
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.
  
VOICE ONE:
  
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
ski areas.
  
(MUSIC BRIDGE)
  
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.
  
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 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.
  
(THEME)
  
VOICE ONE:
  
This SCIENCE IN THE NEWS program was written and produced by Cynthia Kirk
. This is Steve Ember.
  
VOICE TWO:
  
And this is Bob Doughty. Join us again next week for more news about science
in Special English on the Voice of America.