This document discusses air pressure and how it relates to weather. It defines different types of barometers used to measure air pressure, such as mercury and aneroid barometers. It explains that air moves from high to low pressure areas, causing winds. Falling air pressure typically means an approaching storm, while rising pressure means clearing skies. Low pressure systems like cyclones cause cloudy, rainy weather as warm air rises and condenses. High pressure systems like anticyclones cause fair weather as cooler, denser air sinks and allows water vapor to evaporate without forming clouds.

1. Air Pressure and Weather
Air pressure is responsible for
creating weather patterns and the
wind associated.

2. BAROMETERS
• A barometer is an instrument used to measure
the air pressure by meteorologist.

3. MERCURY BAROMETER
• Glass Tube open at one end
• Open end rests in a disk of
mercury.
• When AP INCREASES, it
presses down on the mercury
in the dish.
• This forces the mercury up the
tube.
• The amount of mercury that
rises or falls can be measured.

4. ANEROID BAROMETER
• Aneroid means “without liquid”
• Air tight chamber that is
sensitive to air pressure outside.
• When air pressure increases or
decreases, the walls of the
chamber get pushed in or out.
• The chamber is connected to a
needle that rises or falls.
• The amount the needle moves
can be measured.

5. Air Movement and Flow
• Fluids are substances that tend to flow and to
conform to the outline of its container.
• Fluids move from higher pressure toward lower
pressure.

6. Pressure moves from H to L

7. Rising and Falling Barometers
• Falling Air Pressure usually indicates that a
storm is approaching.
• Rising Air Pressure usually means that the
weather is clearing.

8. Northern vs. Southern Hemisphere

9. The condensed water
vapor clings to a solid
particle forming a cloud.
Less room and
the water
vapor starts to
condense.
Warm air at the
surface is less
dense and rises
As air rises it
cools through
the troposphere
Clouds form as
water vapor
condenses
There is more room for
water vapor to fit and
evaporate into the air.
Air Pressure and Weather!
• Falling Air Pressure Indicates that a storm is approaching.

10. Low Pressure Systems - Cyclone
• Air spirals up in a counterclockwise direction.
• CONDITIONS:
▫ Cloudy, Rain, Snow, Overcast Sky
▫ Air is warmer and wetter (Humid) than normal.
▫ Usually Windy – High pressure air travels to
replace lower pressure air creating wind.

11. Low Pressure Systems - Cyclone
• WHY:
▫ Low pressure is associated with air that is warmer
and more humid than normal.
▫ As air rises through the troposphere, it cools and
condenses into clouds.
▫ These clouds can form percipitation over time.

12. Air Pressure and Weather!
• Rising Air Pressure Indicates that the sky is
clearing.
Clouds are
present
Clouds start to
dissipate as
there is
more room
for water
vapor Lots of room for water vapor to exist
as a gas and no clouds present.
Air is more
dense and
falls
As air falls it
warms up in the
troposphere
A clearing sky
associated with High
pressure falling and
warming

13. High Pressure Systems - Anticyclone
• Air spirals downward in a clockwise direction.
• CONDITIONS
▫ Fair weather (clear)
▫ Air is cooler and more dry than normal.
▫ Sunny during the day and clear at night.

14. High Pressure System - Anticyclone
• WHY:
▫ High pressure is associated with cooler more
dense air that is falling to earth.
▫ Clouds are not present because as the air falls
it warms through the troposphere.
▫ Air molecules spread out (as it warms),
allowing water to evaporate.

15. Barometric Chart

16. What are the units we use to measure
air pressure?
• Most weather reports use “inches of mercury”
▫ EX – Mercury level = 30 inches.
• National Weather Service Maps us millibars to
measure air pressure.
▫ EX – 1 inch of mercury = 33.87 inches
▫ EX – 30 inches of mercury = 1,016 millibars

17. What does Air Pressure Look like on a
weather map?
• http://ww2010.atmos.uiuc.edu/(Gh)/wx/sur
face.rxml