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What Causes Our Weather

• I. Factors that cause weather

A. Weather-
Is the present state of our atmosphere.
B. What causes our weather?
1. The interaction between the earths air,
water, land and the sun causes the changes in our
weather.
C. There are 4 factors that determine the type of
weather we will receive
1. Temperature
2. Air Pressure
3. Wind
4. Amount of moisture in the air.
(Humidity!)
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• II. Heat Transfer on Earth

A. The way the earth is heated controls the
characteristics of the atmosphere.
B. Heat moves through earth in three different
ways
1. Radiation
2. Conduction
3. Convection
C. Radiation-
Energy that comes off of the sun and is absorbed
by the earth.
1. When a surface on earth comes into contact
with this radiation it either absorbs it or
deflects it away.
2. If it absorbs it the surface will change it
into heat.
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The transfer of heat when molecules collide into
each other.
D. Conduction-
1. Molecules in hot objects move toward the
molecules in cold objects.
2. Heat is transferred to the colder object until
the molecules are all the same temperature.
3. Ex. Frying pan on a stove.
E. Convection-
The transfer of heat through convection currents.
(Only through a fluid)
1. Hot molecules are less dense than cold
molecules.
2. A hot fluid will rise and a cold fluid will
sink.
3. This causes convection currents.
4. Ex. Water boiling on a stove.
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• III. Air Pressure

The weight of the atmosphere as it pushes down on
earths surface.
A. Air Pressure-
B. Three factors determine air pressure
1. Temperature of the air.
A.) The higher the temperature, the lower the air
pressure.
2. Density of the air. (Elevation)
A.) The higher the density, the higher the
pressure.
3. The amount of water vapor. (Humidity)
A.) The higher the humidity, the lower the
pressure.
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• IV Wind

A. Why do we get different wind systems?
1. Uneven heating of the earth causes different
air temperatures.
2. That can change the air pressure.
3. Wind blows from areas of high pressure to
areas of low pressure.
B. Coriolis Effect
1. This also will affect wind systems.
2. Coriolis Effect-
Is the result of the earths eastward rotation.

3. It pushes winds in the northern hemisphere to
the right (clockwise), and to the left (counter
clockwise) in the southern hemisphere.
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C. The Different Wind Systems
1. Winds are named for the direction they blow
from.
2. There are four global wind zones on earth.
Windless zone of the earth that is located in the
0 to 5 degree latitudes.
A.) Doldrums-
B.) Trade Winds-
Blow from east to west and are located between 5
to 30 degrees North or South latitude.
Northeast or Southeast Trade Winds
C.) Prevailing Westerlies-
Blow from west to east located between 30 to 60
degrees north or south latitude.
Responsible for our weather.
D.) Polar Easterlies-
Blow from east to west and are located between 60
to 90 degrees north or south latitude.
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D. Minor or Local Wind Systems
1. Earth also has some local wind systems that
affect our weather.
Narrow belts of strong winds in the upper
troposphere.
2. Jet Stream-
A.) There are two jet streams in each hemisphere.
B.) They can change position daily.
C.) When they do they have a major influence on
weather.
3. Sea Breeze-
Cold winds blowing from the water to the land.

A.) It is a convection current of wind caused by
the land warming faster during the day than the
water does.
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Cold winds blowing from the land to the water.

4. Land Breeze-
A.) It is a convection current of wind caused by
the land cooling faster at night than water does.

E. Monsoon Winds
1. Monsoon winds- Sea or land breezes that cover
a large area and change direction with the
seasons.
2. There are two types of Monsoon winds
A.) Summer Monsoon- Large sea breezes that bring
a season of heavy rain.
B.) Winter Monsoon- Large land breezes that bring
a season of very dry weather.
C.) Common Monsoon locations are South East Asia
(India), West Africa, and North Eastern South
America.
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• V. The amount of Moisture in the Air

Continuous movement of water between the
atmosphere and the surface.
A. Water Cycle-
1. Water starts off in oceans, lakes, rivers,
glaciers, etc.
2. It then evaporates.
A.) Evaporation-
The process of liquids turning to gas.
3. Then the gas condenses.
The process of a gas turning into a liquid.
B.) Condensation-
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4. When clouds of water become to heavy, the
water precipitates back to earth.
A.) Precipitation-
Water drops that fall from the clouds because the
clouds could no longer support them.
5. Precipitation then replaces water that has
already evaporated.
A.) Ground Water -
Replaces the water that has evaporated.
Runoff
B. Humidity-
The amount of water in the air.
1. Why can air hold water?
A.) Air acts like a sponge.
B.) Holes in the sponge allow it to hold water.
C.) Air holds water in a similar way.
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D.) Water fits into the spaces between the
molecules of air.
E.) When the air cant hold any more water clouds
start to form.
C. Relative Humidity-
Compares the actual amount of water vapor in the
air with the maximum amount of water vapor the
air can hold.
1. Relative humidity is expressed as a .
2. If the relative humidity is 100 the air can
not hold any more water.
When air contains as much moisture as possible. .

3. Saturation-
4. Additional water added to the air will
condense back to a liquid, depending on the
temperature.
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The temperature at which air is saturated and
water vapor in the air condenses.
5. Dew Point-
D. Two things determine relative humidity
1. Temperature of the air.
A.) Warm air can hold more moisture than cold
air.
2. The amount of moisture added or subtracted
into an area.
A.) ex. Bathroom after a shower.
3. When will relative humidity be the highest?

A.) Cold temperatures.
B.) High Water levels in the air.
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