Weather Patterns
Mr. Latzos
Starter
• Match the word with the definition
• Density
atmosphere
altitude
• The distance above sea level
• The amount of mass in a given volume of
substance
• The whole layer of air that surrounds Earth
Key Concepts
Key Terms
Explore Air Pressure
• What does air do to the balloon?
• What happened?
• What can your observations tell you about
the air in the bottle?
Weather Patterns
•The atmosphere is a layer of air that
surrounds Earth. The atmosphere
supports and protects life.
•Air molecules bounce of each other and
anything they touch using force.
•Air pressure is the force of air molecules
pushing on an area. The greater the
force, the higher the air pressure.
Altitude and Density
• Altitude is the distance above sea level.
• As you move higher into the atmosphere
(above sea level), air pressure decreases.
• Density is the amount of mass in a given
volume of a substance.
• At higher altitudes density decreases also
because there are not as many air
molecules pushed together.
Pressure and Air Motion
• Sometimes air pressure can be different at
places that have the same altitude.
• If air pressure were the same in all locations, air
would not move. Air in areas of high pressure
moves to areas of lower pressure.
– For example when you open a bottle of soda you hear
a hissing sound. That is because the air pressure
inside the bottle is lower than the air pressure outside
the bottle. When the bottle is open, the air outside the
bottle moves to the inside of the bottle.
Barometers
• A barometer is any instrument that
measures air pressure.
The Atmosphere has Wind
Patterns
Starter
• True or False?
• Differences in pressure cause the
horizontal movement of air.
• Air pressure and air density increase with
altitude.
• The sun supplies most of the Earth’s
energy.
Key Concepts
Key Terms
The Atmosphere has Wind
Patterns
• Weather is the condition of the Earth’s
atmosphere at a particular time and place.
• Wind is air that moves horizontally, or
parallel to the ground.
– Uneven heating of the Earth’s surface causes
pressure differences, setting air in motion.
– Wind moves from areas of higher pressure to
areas of lower pressure.
Wind
•
Air circulation (wind) is caused by uneven
heating of the Earth’s surface.
1. Sunlight heats an area of the ground that warms the
air. The warm air rises, creating an area of low
pressure.
2. Sunlight heats an area of the ground less strongly.
The cooler, dense air sinks slowly creating an area
of high pressure.
3. Air moves wind across the surface of the Earth,
from higher pressure to lower pressure.
Global Winds
• Global winds travel thousands of
kilometers in steady patterns. Global
winds last for weeks.
• Global winds are caused by uneven
heating between the equator and north
and south poles.
• Global winds travel in routes called global
wind belts.
Coriolis Effect
• Global winds curve because of the Earth’s
Rotation. The Coriolis Effect is the
influence of the Earth’s rotation on wind.
• If the Coriolis Effect did not exist, winds
would blow directly from the poles to the
equator.
• In the Northern Hemisphere, winds curve
to the right, and in the Southern
Hemisphere winds curve to the left.
How does Earth’s Rotation
Affect Wind?
• How did the rotation affect the lines that
were drawn?
• How does this demonstrate the Coriolis
effect?
• How might changing the speed at which
the balloon rotates affect the results?
Global Wind Belts and Calm
Regions
• The Earth’s rotation and it’s uneven
heating cause patterns of wind belts to be
separated by calm regions.
• Calm regions are zones of either high
pressure or low pressure where winds stay
calm.
• Each wind belt and the calm regions that
border it form a giant loop of moving air
called circulation cells.
Calm Regions
•
There are two types of calm regions:
1. The Doldrums are a low-pressure zone
near the equator. Air rises in these regions
producing clouds and heavy rain. Heavy
evaporation in these areas fuel tropical
storms.
2. The horse latitudes are high-pressure
zones located 30 degrees above and below
the equator. Warm air traveling away from
the equator cools and sinks in these regions.
Wind Belts
•
Three global wind belts are located in each
hemisphere:
1. The trade winds blow from the east, moving from
the horse latitudes toward the equator.
2. The westerlies blow from the west. They bring
storms across much of the US.
3. The easterlies blow from the east, moving from the
polar regions. Stormy weather often occurs when
the cold air of the easterlies meets the warmer air of
the westerlies.
Jet Streams
• A jet stream does not travel on the Earth’s
surface. Instead, it flows in the upper
troposphere from west to east.
• Jet streams do not flow in a straight line,
they loop north and south.
• There are two jet streams in each
hemisphere.
Monsoons
• Monsoons are winds that change
direction with the seasons.
• In the winter, the land is cool creating high
pressure and winds blow out toward the
sea.
• In the summer, the land is warmer than
the sea. Winds blow from the sea onto
land, often bringing heavy rains.