Chapter 8- weather patterns

Lesson 1
How Does Air Move?
• Layers of Air
• Convection Currents
• Wind Patterns
Layers of Air
Air is a mixture of gases in constant motion
Differences in air temperatures create winds.
About .8 of the air is nitrogen and about .2 is oxygen. A very small part of the air
is carbon dioxide, water vapor, and other gases.
There are five layers of Earth’s atmosphere:
TroposphereAltitude: about 8–15 km
Stratosphere - Altitude: about 50 km
Mesosphere - Altitude: about 85 km
Thermosphere - Altitude : about 320 km
Exosphere Altitude: about 600 km
Temperature: –55°C
Temperature: 0°C
Temperature: –90°C
Large Temperature Fluctuations
Temperature: 1700°C
As you go up through the five layers, temperatures and air pressure change. Air
pressure decreases as you go up through the atmosphere. This decrease happens
because the gas particles in the air get farther apart and there is less air above you.
Convection Currents
Land gets warm more quickly in sunlight than water does. At night, land cools
faster than water. This causes the air above the land and water to have different
Winds, storms, and all sorts of weather happen because of the different air
Convection currents are also caused by different air temperatures. In
convection currents, gases or liquids rise and sink in a circular path.
In cool air, gas particles are closer together than in warm air. Every liter of cool
air is heavier than every liter of warm air. When the two kinds of air are next to
each other, the cool air will sink and force the warm air to rise.
cause daily
patterns of
clouds, wind,
rain, and air
Wind Patterns
• Six huge convection currents form in the air above Earth.
One reason they form is that tropical regions get warmer
than other parts of Earth.
• The moving of the huge convection
currents combines with the spinning
of Earth to cause regional surface
wind patterns.
• Jet streams are high above the
ground between these huge
convection currents. A jet stream is
a band of very fast wind formed by
the different temperatures between
the convection currents.
Lesson 2
• Properties and Kinds of Air
• Four Air Masses
• When Air Masses Meet
Properties and Kinds of Air Masses
• Air that stays over an area for some time takes on
properties of that area and becomes
an air mass.
• An air mass is a large body of air with similar
properties all through it. The most important
properties are temperature and amount of water
vapor. An air mass
keeps its original properties for a while as it moves.
• The kind of weather you have at any time is because
of the air mass in your area.
Four Air Masses
1) Maritime Tropical Air
Humid air has lots of
moisture. Over
tropical oceans or
rainforests, an air
mass becomes warm
and very humid
because water can
easily evaporate there
2) Maritime Polar Air
Even though the
ocean near the
poles is cold, water
vapor evaporates
into the air. An air
mass forming over
the poles is cold
and moist.
3) Continental Tropical
Air A large hot desert
can cause the air above
it to be warm and fairly
4) Continental Polar
The land near the
poles is not very
moist. So, the air
mass from this
area is cold and
fairly dry
When Air Masses Meet
• A front is a boundary between two air masses.
• A cold front brings colder air into an area. A
warm front brings warmer air into an area.
• Rising air at fronts often causes rain or snow.
Lesson 3
• Thunderstorms
• Tornados
• Hurricanes
• Stage One- strong, quickly upward currents of
moist air. Clouds grow.
• Stage Two- Precipitation starts to fall, which pulls
air down with it. There is upward and downward
air movement.
• Stage Three- All air currents are moving
downward. Clouds get smaller as more
precipitation falls.
• Lightening is a large electrical spark moving
between areas of opposite electrical charge.
• Layers of wind form from wind moving at
various speeds in different directions.
• A column of spinning air is formed between
the layers of wind.
• Upward winds push one end of the column up
and downward winds push the other end
down creating a funnel called a tornado.
• Tornados form quickly and last only a few
• Hurricanes get their energy from warm ocean
• Hurricane winds are not as fast as a tornado
but they can cause more damage because
they can last for days and they are very large
Lesson 4
• Collecting Data
• Weather Forecasts
• Weather Maps
Collecting Data
• A weather system is described in terms of
temperature, moisture, clouds, precipitation, air
pressure, wind speed, and wind direction.
• Various instruments are used for forecasting the
A barometer shows air pressure
An anemometer measures wind speed
A hydrometer measures the moisture in the air
A rain gauge measures how much rain has fallen
A radar measures winds and precipitation inside a
Weather Forecasts
• Weather forecasters observe many patterns of
weather change
. They use this information to make inferences
that help them to predict what weather will
be like in the future.
Weather Maps
• Forecasters use weather maps to show
current weather conditions and their
Lesson 5
Weather and Climate
• Climate is the average weather conditions over a
long period of time, usually 30 years
• Climate includes such things as average amount
of precipitation, average temperature, and how
much the temperature changes over the year.
• Fossils have helped scientists make assumptions
about ancient climates

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