“ What Causes Our Weather”
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I. Factors that cause weather :
A. Weather- Is the present state of our atmosphere.
B. What causes our weather?
1. The interaction between the earth’s 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.
D. Conduction- The transfer of heat when molecules collide
into each other.
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 earth’s surface.
B. Three factors determine air pressure:
A. 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 earth’s eastward
rotation.
3. It pushes winds in the northern hemisphere to the right
(clockwise), and to the left (counter clockwise) in the
southern hemisphere.
C. The Different Wind Systems:
1. Winds are named for the direction they blow from.
2. There are four global wind zones on earth.
A.) Doldrums- Windless zone of the earth that is
located in the 0 to 5 degree
latitudes.
“Northeast B.) Trade Winds- Blow from east to west and are
or Southeast
located between 5 to 30 degrees
Trade
North or South latitude.
Winds”
C.) Prevailing WesterliesBlow from west to east locate
Responsible for our
weather.
D.) Polar Easterlies-
between 30 to 60 degrees nor
or south latitude.
Blow from east to west and are
located between 60 to 90 degrees
north or south latitude.
D. Minor or Local Wind Systems:
1. Earth also has some local wind systems that affect our
weather.
2. Jet Stream- Narrow belts of strong winds in the
upper troposphere.
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.
Cold winds blowing from the land to
the water.
A.) It is a convection current of wind caused by the
land cooling faster at night than water does.
4. Land Breeze-
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:
A. Water Cycle-
Continuous movement of water between
the atmosphere and the surface.
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.
B.) Condensation-
The process of a gas turning into
a liquid.
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.
D.) Water fits into the spaces between the molecules
of air.
E.) When the air can’t 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.
3. Saturation- When air contains as much moisture as
possible. .
4. Additional water added to the air will condense back to
a liquid, depending on the temperature.
5. Dew Point- The temperature at which air is saturated
and water vapor in the air condenses.
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.