Air Pressure
= the weight of the air above
you from where you are to the
top of the atmosphere.
Air is
compressible • Half of all air
molecules are
below 18,000 feet
of altitude; 3/4
are below 36,000
feet, etc.
• At sea level air
exerts a force of
about 14 pounds
per square inch
(enough to crush
the soda can.)
measured with
a barometer
Air Pressure in
the News -
Cold air has
pressure
• higher
Cold air is more dense,
so it
sinks down and pushes harder.
– Barometer goes?
• Hot air expands, becomes less
dense, rises, and exerts less
pressure.
– Barometer goes?
=
movement
• Wind always goes from an area of
ofpressure
airtoward an area of
high
lower pressure.
• Wylie’s Law - You can’t push with
rope; you can’t pull with air!
• Wind direction is described by
where the air comes from - a west
wind blows from west toward the
Which way would
the wind blow?
What time of day is shown in this picture?
WindsWhich way would
the wind blow?
What time of day is shown in this picture?
meteorologists
predict wind
direction?
learned about
Coriolis
• Because the Earth rotates on its axis, things
moving from North to South or from South to
North are deflected.
• In the Northern Hemisphere, the deflection is to
the right.
• In the Southern Hemisphere, the deflection is to
the left.
Figure 3.16
Throwing a ball to someone on a merry go-round does not get to them,
they have moved.(a) The equator travels faster than at the poles, it
takes a day for both of them to make one full revolution.
Winds Around
Pressure Systems
more look at that
map.
System Over
Iceland
Why don’t high
pressure systems
show up on satellite
photographs?