The Atmosphere in Motion
A Video Lesson from
Exploring Weather
A Unit of Study
Teacher’s Guide
catalog #2383
Video Production,
Scripts, Teacher’s Guide:
John Colgren
Consultant:
James Vavrek
Spohn School
Weather Station
Hammond, Indiana
Severe Storm Footage:
Gene Rhoden
Roy Britt
Robert Prentice
Television Meteorologist:
Alan Sealls
WGN-TV, Chicago
Published & Distributed by…
AGC/UNITED LEARNING
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Suite 100
Evanston, IL 60201
1-800-323-9084
24-Hour Fax No. 847-328-6706
Website: http://www.agcunitedlearning.com
E-Mail: info@agcunited.com
THE ATMOSPHERE IN MOTION
A Video Lesson from
EXPLORING WEATHER
A Unit of Study
Time: 20 minutes
INTRODUCTION
This video is designed for use in grades 5 through 9. It introduces
students to the major ideas and concepts associated with the study of
weather. The sun and moisture are shown to be the driving forces
behind our planet’s weather.
PROGRAM OBJECTIVES
After viewing the video and participating in various activities, the
students should be able to achieve the following objectives:
• Identify the sun and moisture as the driving forces
behind weather.
• Recognize how weather influences our lives.
• Identify that air masses form over different
regions and take on characteristics of those regions.
SUMMARY OF THE VIDEO
The weather is driven by two very important things: the sun and
moisture. The sun is the source of almost all the energy used on earth.
Energy from the sun warms the planet, causes winds, snowstorms, and
even rain. The sun is at the center of our planet’s water cycle. The tilt
of the earth is responsible for the seasonal changes we experience. Air
masses develop over areas of the planet. The air masses have different
moisture content depending upon where they form. Over the water,
the air masses collect a lot of moisture. Over land, the air masses are
dry. Air masses move from location to location.
INTRODUCING THE VIDEO
Weather affects our daily lives from what we wear to even how we
feel. The earth’s weather is driven by the energy of the sun. This
energy is the force behind the water cycle which puts moisture into the
atmosphere.
FOLLOW-UP ACTIVITIES
1. Layers of the Atmosphere is provided as additional information concerning the atmosphere.
2. Warm Air Rises is an experiment to show that warm air rises.
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3. Slanted Rays is an experiment designed to show the difference
between slanted and direct rays of sunlight.
4. Heating of the Earth is an experiment designed to illustrate how
the slant of sunlight affects the area illuminated by a flashlight.
5. Ice, Water, and Steam is an experiment set up to show the
temperature changes that occur when water changes from a solid
to a liquid and then a gas.
6. Distance and Radiant Energy is an experiment used to
determine how distance from the source of radiant energy affects
temperature.
7. Warming and Cooling of Different Substances compares soil,
sand, and water with respect to their ability to warm up and cool
down.
DISCUSSION
Discuss how the earth is heated unevenly and how the earth’s tilt and
rotation provide us with seasonal changes. Illustrate this further using
a filmstrip projector as the sun. Position the filmstrip projector in the
center of the room and put a student in charge of turning the light
toward a globe which you hold while moving in a large circle around
the sun. Put the globe at a 24 degree tilt to represent the earth’s tilt.
Keep the globe tilted in the same direction as you move around the
sun. Ask the class to determine what season is represented at each of
the four corners of the earth.
•
•
•
ANSWER KEY
LAYERS OF THE ATMOSPHERE
Information sheet.
WARM AIR RISES
Observations:
1. The balance moves up on the side where the candle heat rises
into the bag.
2. Student drawing.
Conclusions:
The bag above the candle moves up after the warm air from the
candle rises into the bag. The imbalance of the bags shows that the
warm air is lighter.
SLANTED RAYS
Observations:
The paper on the ground should feel warmer. Be sure this
experiment is performed close to noon with the sun overhead.
Conclusion:
The paper on the ground receives more direct rays of sunlight. The
other paper is at a slant; the rays are spread out.
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•
•
•
•
HEATING OF THE EARTH
Observations:
The answers will vary depending on the size of the graph paper and
the height of the flashlight. However, the slanted flashlight rays
will cover more squares than the light from the flashlight held
directly above the graph paper.
Conclusions:
1. The light from the slanted flashlight covers more area than
the direct flashlight.
2. The direct flashlight would produce greater heat because the
same energy is concentrated into a smaller area.
ICE, WATER AND STEAM
Observation:
While ice is present, the temperature will stay very close to zero.
When the ice is gone, the temperature will rise until it reaches 100˚
degrees Celsius. Then, while boiling occurs, the temperature will
remain near 100˚ Celsius.
Conclusions:
1. Ice melts at 0˚ Celsius.
2. Water boils at 100˚ Celsius.
3. While the ice is melting, the temperature will remain constant,
for the heat energy is being used to change the state of ice
from a solid to a liquid.
DISTANCE AND RADIANT ENERGY
Students should find that the temperatures vary as you move away
from the source of heat. The closest thermometer will have higher
temperature readings.
WARMING AND COOLING OF DIFFERENT SUBSTANCES
Students should discover that the soil and sand warm up faster than
the water, but the water retains the heat longer.
SCRIPT OF VIDEO PRESENTATION
THE ATMOSPHERE IN MOTION
We live at the bottom of an ocean…
Not an ocean of water,
But an ocean of gases we call our atmosphere.
The atmosphere is a mixture of gases, liquids, and even tiny suspended solids. It is 78% nitrogen, 21% oxygen, and the final 1% is
made up of eighteen other gases including water vapor, neon, argon,
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carbon dioxide, helium, hydrogen, methane, krypton, ozone, ammonia, and iodine.
There are also foreign substances in the air such as industrial smoke,
dust, waste gases from cars and trucks, volcanic ash, and a fine rain
of meteoric sediment from space.
The atmosphere extends hundreds of miles above the earth’s surface
but it is thickest in the lowest level near the surface called the
troposphere. This is where all our weather occurs. This is also where
we live.
Weather is driven by two things. The sun and moisture. Let's look at
how the sun affects weather first.
The sun is the source of almost all the energy used on earth. Energy
from the sun warms the earth and provides us with light.
Energy from the sun causes winds.
Energy from the sun causes snow.
Even rain is caused by the sun’s energy.
The energy from the sun that reaches earth is only a very small amount
of the energy released every second by the sun. The sun’s energy goes
out in all directions. Yet that energy is enough to heat our planet and
maintain life forms.
The energy from the sun is called solar energy or solar radiation. Heat
and light may be the most obvious forms of radiant energy, but there
are others present which are invisible to our senses. The energy from
the sun comes to earth in the form of electromagnetic waves called
radiation.
A small part of the sun’s energy that comes in contact with the earth’s
atmosphere is reflected back into space when it hits dust and water
particles.
Some of the radiant energy is scattered throughout the atmosphere.
Harmful gamma rays, x-rays and some of the ultraviolet rays are not
allowed through the atmosphere. We are protected from these
harmful rays by the filtering effect of the atmosphere. About 10 to 30
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miles above the earth is the naturally occurring ozone layer, which
absorbs much of the sun’s ultraviolet radiation. It shields us from
these harmful rays.
Part of the sun’s energy reaches the earth’s surface where it is
absorbed or reflected.
How much energy is absorbed depends on the type of surface the
energy strikes, the angle of the sun, and the intensity of the sunlight.
Snow and ice reflect radiant energy, while soil and rocks tend to
absorb energy.
Think of how hot an asphalt parking lot can get on a warm, clear,
sunny day.
Or have you ever touched a car that has sat in the hot summer sunlight
all day?
Dark objects, like the asphalt and dark colored objects like the car, can
absorb a lot of energy.
Heat moves from one place to another by one of these three methods.
Radiation is heat transfer by electromagnetic waves. When standing
in front of a fireplace, the side facing the fire is warmed, while the
other side of a person’s body seems cool.
Conduction transfers heat by contact. Transfer is always from warmer
to colder regions.
A spoon becomes hot to the touch while sitting in boiling soup because
of conduction.
The third method of heat transfer is convection. Convection is the
transfer of heat through a fluid caused by motions which mix and
transport energy. Look at the noodles moving about in this pot of
heated water.
Together, all three forms of heat transfer work to circulate energy in
the atmosphere. Heat energy from the sun, in the form of radiant
energy, travels through space by radiation.
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The radiant energy warms the surface of the earth. Air near the earth
is heated by conduction. The heated air expands and becomes less
dense than the surrounding cooler air. This expanded warm air is
buoyed upward and rises.
Cooler, heavier air flows in to replace the rising air. Then, this cooler
air becomes heated and the whole cycle starts again. The movement
from rising air, to spreading out, to falling cool air, creates wind. This
circulates energy throughout the atmosphere.
Temperatures around the earth vary greatly. Temperatures at the
North and South poles are much lower than the temperatures at the
equator. This occurs because of the earth’s tilt--the angle of the earth
to the sun. The earth spins on an imaginary axis.
The earth is tilted on its axis at an angle of 23.5 degrees. This tilt is
responsible for our seasons and the temperature differences. When
the Northern Hemisphere is tilted away from the sun, then the
Southern Hemisphere is tilted towards the sun. So the Northern
Hemisphere receives less radiant energy and experiences winter,
while the Southern Hemisphere has summer.
The number of hours of sunlight help to determine how much radiant
energy is absorbed by the earth’s surface. When tilted away from the
sun, there are fewer hours of sunlight.
The other thing that influences the amount of energy is the angle of the
sun’s rays. We can illustrate this idea with a flashlight and some graph
paper.
When the light strikes the paper at a 90 degree angle, the light is
concentrated.
When the flashlight is at an angle, a larger area is covered by the light.
This same amount of light is then spread out over a larger area so less
of it strikes any given point. The same thing happens with the rays of
sunlight.
At the equator, the rays are more direct than at other locations.
Temperatures near the equator are warm throughout the year…
So, the length of daylight and the angle at which the sun’s radiant
energy strikes the earth changes from day to day and season to season.
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The earth is divided into climate zones based on the amount of radiant
energy received by regions of the earth.
Climate is the average weather conditions of an area--daily and
seasonal weather events over an extended period of time.
Remember, there are two driving forces that affect weather: the sun
and moisture. Let's look at moisture now.
Water vapor is an important part of the earth’s atmosphere. Water
vapor is the gaseous form of water. To understand how the moisture
or water vapor gets into the air you must understand the water cycle.
The amount of water on our planet is a finite amount.
Though three-fourths of the surface is covered by water, only 3% of
the earth’s water is fresh water.
For billions of years the earth’s water has been recycling through a
process called the water cycle. The cycle is powered by energy from
the sun. Heat energy causes water in the oceans, lakes and soil to
evaporate. The heat causes molecules to move faster and farther apart.
The liquid water may change to a gaseous state called water vapor and
rise into the atmosphere.
Moisture is also added to the atmosphere when plants release water
vapor from their leaves in a process called transpiration.
As the water vapor rises in the atmosphere and cools, clouds begin to
form. If cooling continues, the water vapor may condense into water
droplets or ice crystals.
As the cooling continues, the water returns to the earth as precipitation.
This precipitation is fresh water because when ocean water or tainted
water evaporates, only fresh water vapor is released. Other particles,
such as salts, are too heavy to evaporate.
So through the water cycle, moisture is added to the atmosphere and
ultimately water is recycled so that we have fresh water. Much of the
earth’s fresh water is found as ice and snow.
Now let's turn our attention to how weather systems move from place
to place.
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Watch weather reports for a few days and you will probably see
weather systems move from one location to another.
Weather conditions change from day to day because of the movement
of air masses.
An air mass is a large body of air that takes on characteristics and
conditions similar to the area that the air mass forms over.
Air masses can form over land or over water, and either in polar
regions or in the tropics.
Here is a map that shows the common air masses that affect the
weather for the continental United States.
Air masses take on the characteristics of the area in which they form.
The continental polar air mass would be cold, dry air. The air mass
over water in the tropics is moist, warm air. Air masses forming over
water are moist and air masses forming over land are dry.
Air masses move from one location to another because of wind. Wind
is air in motion. It is put into motion by the energy of the sun. Some
parts of the earth are heated more than others by the sun. The air above
these hot spots is warmed and rises because it is less dense than
surrounding air.
Here is a simple demonstration that shows why warm air is less dense
than cold air. A small amount of air is blown into the balloon and then
the balloon is stretched over the mouth of the bottle. As the air in the
balloon and bottle is heated, the balloon expands. Air molecules move
faster and more vigorously when heated. Because of this increased
energy and motion, the molecules bounce around and move farther
away from each other. The balloon expands as a result of this activity.
Warm air is less dense than cold air because the molecules of warm
air spread out and require more room than molecules of cold air. Air
molecules are held close to the earth by gravity. If we weigh a column
of air one inch square from sea level to the top of the atmosphere, it
weighs almost 14.7 pounds. If more air molecules are packed into the
column, the weight goes up and the pressure increases; so cold, dense
air has greater pressure than warm air, which is less dense. Winds
always move from areas of high pressure into areas of low pressure.
So, cold, dense air moves to the low pressure areas of warm air.
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On a weather map, there are areas identified with an H for high
pressure and areas marked with an L for low pressure. The thin lines
on the map are called isobars. They connect weather stations with the
same pressure readings. The numbers are in special units called
millibars of pressure.
On a warm summer day at the beach you may have felt a cooling
breeze. This happens because the land heats up faster than the water.
As the air above the heated land rises, then the cool air over the water
moves in to replace it. At night the opposite happens--the water holds
onto the heat longer than the land, so the air above the water is heated
and rises as cool air above the land sinks and moves out from the land
to the water. The sea breeze winds only affect a small region.
The air above the equator is heated and forced upwards by the colder,
denser air that moves in underneath it. The warmer air moves towards
the North Pole while cooler air from the North Pole moves south. If
the earth didn’t rotate, this movement of warm air north and cold air
south would be the circulation pattern for our planet in the Northern
Hemisphere. In the Southern Hemisphere, the warm air of the equator
would rise and move south toward the South Pole while the cold air
of the South Pole would move north.
However, the earth does rotate and as a result, winds are bent to the
right north of the equator and to the left south of the equator. This is
called the Coriolis effect and it can be illustrated by thinking of a
rocket launched from the North Pole toward New York City. Because
the earth spins, the rocket would land in Chicago.
We will use this turntable to illustrate the Coriolis effect. If the marble
is released, it rolls across the turntable in a straight line. However, if
the turntable is moving, the marble curves to the right.
As the heated air from the equator rises high into the atmosphere, it
moves towards the poles. As this air moves away from the equator,
it cools and sinks. When it reaches the surface again, some of it moves
back toward the equator and some continues to move toward the
poles. As a result of this air movement, a series of prevailing winds
are formed.
As you can see, the continental United States is affected by the
prevailing westerlies. Weather moves generally from the west to the
east in the United States.
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Local weather is brought into an area by the prevailing winds. The
weather conditions depend on the characteristics of the air mass that
is moved by the prevailing winds.
When air masses meet, a boundary forms between the air masses. The
masses don’t mix, but instead, one mass pushes the other along. This
boundary is called a front.
A cold front forms when a cold air mass pushes a warm air mass.
Because the cold air is denser than the warm air, the warm air is pushed
up quickly. As the warm air rises quickly, the moisture in the warm
air cools and condenses. The water vapor changes to tiny drops of
liquid water. Clouds form as a result of this cooling.
The clouds that form are usually cumulus clouds. The size of the
clouds depend on the amount of moisture present in the warm air
mass. Precipitation is often heavy along a cold front. It may not last
long, but it is generally a heavy rain with increased wind speed.
Thunderstorms are common along cold fronts. During the winter,
snowstorms and blizzards may occur along a cold front, depending on
the temperature differential and the amount of available moisture.
A warm front occurs when a warm air mass pushes a cold air mass.
The warm air moves up and over the cold front. Notice that the
movement of the warm air over the cold is at a much more gradual
slope than at a cold front. The warm air does not rise as fast as it does
in a cold front so the clouds that form are different. They are thinner
and spread out over a greater area. These clouds are called stratus.
These high clouds are a sign that a warm front is approaching.
A warm front moves through an area much slower than a cold front.
The clouds associated with warm fronts are thick, low clouds that
produce a steady light rain. This may last for a day or more.
Sometimes the boundary between a cold and warm air mass doesn’t
move. In that case, it is referred to as a stationary front.
Sometimes when a cold front is overtaking a warm front, the warm
front is actually lifted above the ground. This may create drastic
temperature changes and violent weather. This type of rare front is
called an occluded front.
So air masses moving from areas of high pressure to areas of low
pressure bring weather from one location to another. Air masses take
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on the characteristics of the areas over which they form. As air masses
make contact with each other, warm and cold fronts are formed.
Clouds and precipitation may result.
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AGC/United Learning
1560 Sherman Avenue, Suite 100
Evanston, Illinois 60201
(800) 323-9084, Fax (847) 328-6706
http://www.agcunitedlearning.com
e-mail: info@agcunited.com
The Atmosphere in Motion
Exploring Weather-A Unit of Study
Catalog #2383
ISBN No. 1-56007-319-5