Air
Earth’s Atmosphere
Atmospheric Pressure
* The weight of the air above
you. The more air that is above
you the more pressure you will
feel.
* Sinking air pushes down
more- cold air is usually high
pressure.
* Rising air pushes down lesshot air is usually low pressure.
Where is pressure greater, at top of a
mountain or at sea level?

Sea level
So ….

Atmospheric pressure is greatest near Earth’s surface

Decreases as you move out to space

Can vary from locations at the same level due to the density of the air
Cold Air vs. Warm Air

Cold air is denser than warm air so has a higher pressure

Warm is less dense so has a low pressure

These masses of warm/cold air used to predict weather
Barometer

Measures air pressure

Measured in millibars
Movement of Air
 Wind
 The
movement of air molecules from an area of high
pressure to an area of low pressure
 Temperature
differences on Earth’s surface create
areas of different pressure and the winds that
circulate our planet
Causes of temperature difference

Earth is curved rather than flat so
more solar radiation is received at
the equator

Air above equator is heated more
than any place on Earth … heated air
rises (low pressure)

Air above poles receives less
radiation so air is cooler … colder air
sinks (high pressure)
The Coriolis Effect

Due to Earth’s rotation

Causes air masses moving south in
Northern Hemisphere to be turned
westward from their original paths

These wind patterns determine the
weather and also when ships/planes
can travel
Review …..

What 2 things determine our wind patterns on Earth ?

Differences in heating

Coriolis effect
Global Wind Systems
Trade winds
Westerlies
Easterlies
Doldrums
Jet Streams

Located near top of troposphere

Flow west to east

2 jet streams in each hemisphere

Resemble fast moving rivers

Average speed between 97-185 km/h

Their positions in altitude and latitude from day to day / season to season
Jet Stream
Local Wind Systems

Land Breezes


Movement of air towards water
Sea Breezes

Movement of air towards land
Mountain vs. Valley Breezes

During DAY, heated air along mountain slopes rises = Valley Breeze

At NIGHT, cooled air along mountain slopes moves downward = Mountain
Breeze