The Earth’s Atmosphere: Factors
That Affect the Weather
SOL 6.6
• We have learned that virtually all
of Earth’s weather takes place in
the lowest level of the
atmosphere called the
troposphere.
• This is due in part to the amount
of heat, water, and air pressure
found at this level.
• Heat energy, water
vapor, and air pressure
determine the weather
conditions on Earth.
• Let’s investigate how these three
factors determine the weather.
• We know that the unequal
heating of the Earth’s surface by
the sun causes a rising and falling
air pattern called convection.
(vertical movement)
•Convection distributes
heat energy in the
troposphere as warm
air rises and cooler air
falls.
• In addition to rising and falling, air also
moves horizontally.
• This horizontal movement is caused by
differences in air pressure.
• Air tends to move from areas of high
pressure to areas of low pressure.
• This horizontal movement of air due to air
pressure is called wind.
• These vertical and horizontal
movements of air are connected.
• This is true because differences in
air pressure are caused by the
unequal heating of the Earth’s
surface.
• When an area of the Earth is heated by the sun,
the air above it heats up, too.
• As air heats up, it expands, becomes less
dense, and rises.
• Cooler, heavier air nearby will then move
horizontally (wind) under the heated air causing
it to rise even more.
• The greater the pressure differences are
between two locations on Earth, the faster the
winds.
• Added to this moving mix of heat and pressure is water
vapor.
• The amount of water vapor or moisture in the air is called
humidity.
• As the bodies of water on Earth are heated by the sun,
water molecules escape into the air in the form of water
vapor (evaporation).
• This water vapor rises with the heated air in a convection
current into the troposphere.
• As this humid air rises into the cooler regions of the
troposphere, the water vapor cools down and changes
into minute, condensed water particles.
• As more and more of these condensed water particles
join together, a cloud is formed.