Name: __________________________________________________________ Date: 11/4/15 Period: ______ ASSIGN
Notes: Weather Patterns Chapter 2.1 and 2.2
What is air pressure?
• Air pressure is the force of air molecules pushing on an area.
• The greater the force, the higher the air pressure
• Air molecules move in all directions so air pressure pushes in all directions.
• Air pressure at any area on earth depends on the weight of the air above the
area.
How is air pressure
1. The higher the altitude = lower the density of air
related to altitude
2. The lower density of air = less air pressure
and density?
SO:
3. The higher the altitude = less air pressure
• The air at sea level is denser than air at high altitudes.
Draw air pressure at
sea level vs. on a
mountain.
How does
temperature relate to
air pressure?
How does air move?
Review: Convection
Currents
What is a barometer?
What is weather?
What is wind?
How does wind form?
Summarize: How does
wind move?
What are global
winds?
Where air is heated, the molecules move faster, the air becomes less dense,
and the air pressure decreases.
• This is called a low-pressure area
• Where the air is colder, molecules move slower, the air becomes denser, and
the air pressure is greater.
• Called a high-pressure area
• Air pressure is often different in two locations at the same altitude.
• Because of differences in air pressure, air starts to move from areas of
higher pressure toward areas of lower pressure.
• The air may move only a short distance, or may travel many kilometers.
• Ex. Balloon - open a balloon and the air rushes out to an area of lower
pressure
• Ex. Tires - air escapes when punctured
• Convection: the movement of energy from place to place by the flow of a
heated material.
• Warm water or air is less dense so it rises.
• Cool water or air is more dense so it sinks. It moves in and helps push up
warm air or water.
• A barometer is an instrument that measures air pressure.
• The flexible chamber on the barometer contracts (gets smaller) when the air
pressure increases.
• The chamber expands (gets bigger) when the air pressure decreases.
• Weather is the condition of Earth’s atmosphere at a particular time and
place.
• Wind is a very important part of weather.
• Wind is air that moves horizontal or parallel to the ground.
• Uneven heating of Earth’s surface causes such pressure differences, which
set air in motion.
• Sunlight is concentrated near the equator because it strikes the surface
directly.
• Sunlight is more spread out near the poles because it strikes at a lower
angle.
• The air moves as wind across the surface, from higher toward lower pressure.
• Depending on the difference between the pressures, the force of wind will be
different
• Small pressure differences cause slow winds, may be barely noticeable.
• Large pressure differences cause fast winds - can uproot trees.
1. The air is heated and rises. This creates a low pressure area.
2. Cool air sinks. This causes a high pressure area.
3. Wind move from the area of high pressure to an area of low pressure
• Global winds travel 1000s of km in steady patterns.
• Uneven heating between the equator and north and south poles causes
global winds.
• If the Earth did not rotate, global winds would flow directly from the poles to
the equator.
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How does Earth’s
rotation effect wind
direction?
What are global wind
systems (belts)?
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What are the calm
areas between the
wind belts called?
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What is a circulation
cell?
What are jet streams?
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Earth’s rotation changes the direction of winds and other objects moving
over the Earth.
Coriolis Effect- the influence of Earth’s rotation on winds (only noticeable in
long distances)
In the N. Hemisphere, winds curve to the right in the direction of the motion.
Winds in the S. Hemisphere curve to the left.
Because the Coriolis Effect causes global winds to curve, they cannot flow
directly north and south.
Instead, global winds move along three routes in each hemisphere:
1. Trade winds:
 0-30 degrees N & S of equator, between equator and horse latitudes
 move east to west
2. Westerlies:
 30-60 degrees N & S of equator
 move west to east
 Responsible for movement of most weather across U. S. and Canada
3. Polar Easterlies:
 60-90 degrees N and S of equator
 Move east to west
Storms often occur when the cold easterlies air meets the warm westerlies
air
Doldrums: low pressure zone near the equator. Warm air rises and spreads
out toward the poles. Clouds and heavy rains are produced. In the hottest
months this air movement causes tropical storms
Horse Latitudes: high pressure zones approximately 30 degrees north and
south of the equator. Warm air leaving the equator cools and sinks in this
region. Weather is cool and dry in this region.
Circulation cell: A giant loop of moving air made of a wind belt and the calm
regions that border it.
The section of a cell that flows along Earth’s surface is global wind.
Jet streams usually flow in the upper troposphere from west to east for
1000s of km.
Each hemisphere has two jet streams, a polar jet stream and a subtropical
jet stream.
The polar jet stream has a strong influence on weather in North America.
Scientists must know where the jet stream is flowing to make accurate
weather predictions.
Questions:
1. How does the movement of air molecules cause pressure?
2. How does altitude affect air pressure?
3. How is air density related to air pressure?
4. Two barometers are placed one kilometer apart. One shows higher pressure than the other. What will
happen to the air between them?
5. What factor determines the strength of wind? ____________________________________
6. What causes wind?
7.
8. What is the Coriolis Effect?
9. In the Northern Hemisphere, winds curve to the _______________, while in the Southern Hemisphere,
winds curve to the ______________.
10. In what direction do jet streams generally flow?
11. List the 3 global wind belts.
12. What is a circulation cell?