19.1 Understanding Air
Pressure
What is Air Pressure?
 The force exerted by the weight of a column of air
above a given point
 Exerted in all directions
 The air pressure pushing down on an object exactly
balances the air pressure pushing up on the object
 Barometer – used for measure air pressure
 Air pressure rises, mercury in the tube rises (and opposite)
Factors Affecting Wind
 Wind is the result of differences in pressure
 Air flows from areas of higher pressure to areas of lower
pressure
 The unequal heating of Earth’s surface generates
pressure differences
 Solar radiation is the ultimate energy source for most
wind
 Named based off what direction it comes from
Continued…
 3 Factors combine to control wind
 Pressure Differences
- Pressure Gradient
- Closely spaced isobars indicate a steep pressure gradient &
high winds.
- Widely spaced isobars indicate a weak pressure gradient &
light winds
 Coriolis Effect
 Friction
- Slow air movement (changes wind direction)
- Most prominent features of airflow high above the friction
layer is the jet streams
In a high pressure area,
air will (rise, sink)
because the air is
(less, more) dense.
This is because the air is
(cold, warm)
and (rises, sinks).
Therefore, clouds CANNOT form.
In a low pressure area,
air will (rise, sink)
because the air is
(less, more) dense.
This is because the air is
(cold, warm)
and (rises, sinks).
Therefore, clouds are
LIKELY to form.
low
pressure
warm or cold air
air rising or sinking
clouds or no clouds
clockwise or
counterclockwise wind
direction
winds toward or
away from the center
high
pressure
Review Questions
 What is the ultimate energy source for most wind?
 Why do jet streams flow parallel to isobars?
 How does the Coriolis effect influence motion of freemoving objects?