1. Air Pressure
The pressure
exerted on an
object by the air.
– Occurs in all
directions up,
down, sideways
2. Air Pressure
A barometer is used
to measure the
amount of pressure
in the air.
– Units = mmHg
(millimeters of
Mercury) or atm
(atmospheres)
3. Barometers
Rapidly falling pressure almost always
means an approaching storm system.
Rapidly rising pressure almost always
means clearing and cooler weather is
ahead.
4. Winds
Winds are created
by horizontal air
pressure
differences –
pressure gradients
Uneven heating of
the Earth creates
pressure
differences
5. What affects wind?
Pressure differences- Cause air to
move
The Coriolis Effect- causes global
winds to be deflected
Friction- slows down air, which
changes wind direction
6. Measuring Pressure
Isobars- lines of equal pressure
– Much like contour lines, but instead of
elevation, they are lines of equal pressure
– Are used to predict where weather is
moving
7. Jet Stream
Fast flowing,
relatively narrow
air currents found
just under the
tropopause
Form at the
boundaries of
adjacent global
wind belts
8. Global Winds
Global winds are
created by the
unequal heating of
Earth.
The equator is
much hotter than
the rest of Earth,
causing an
extremely low
pressure.
9. Global Winds
This causes air from
adjacent areas to
move towards the
equator.
This movement
begins a chain
reaction of air
movement
throughout Earth,
creating 6 wind
belts.
10. High Pressure Zone/Cyclone
Occurs when
temperatures are cold
Little or no moisture
(humidity)
– The air is heavy and sinks
towards Earth’s surface
Winds move outward and
clockwise around the
center of a cyclone
11. Low Pressure Zone/Anticyclone
Occurs when
temperatures are warm
Can have large amounts of
moisture (humidity)
– The air is light and rises
upward into the atmosphere
Winds move outward and
counterclockwise around
the center of the
anticyclone
12. The Coriolis Effect
The Coriolis effect is a
result of the spinning of
Earth.
As Earth spins, anything
moving in a straight line
from North to South will
be deflected sideways.
– In the Northern
Hemisphere, winds,
water, and other fluids
will be deflected to the
right at a 90o angle.
– In the Southern
Hemisphere, everything
will be deflected to the
left at a 90o angle.