1. AIR PRESSURE, AIR MASSES AND FRONTS
Earth Science

2. Air Pressure
Air Pressure: The weight of the air pushing down on the surface of earth.
Barometer:
The tool that measures air pressure.

3. High and Low Pressure Systems
High pressure is caused by Cool, Dry air SINKING.
Low pressure is caused by Warm, Moist air RISING.
Cool, Dry Air
= High Pressure
= Clear Skies
Warm, Moist Air
= Low Pressure
= Cloudy Skies

4. ISOTHERMS
Isotherms: Lines connecting place of equal temperature

5. Pressure Centers
Isobars: Lines on a map connecting places with equal pressure. This shows you the area of High and Low Pressure.
Arrows show direction of wind.

6. DRAWING ISOBARS •
000 •

7. Prevailing Westerlies
Global Winds
Global Winds: the global circulation of air from HIGH pressure to LOW pressure.
THE WINDS WILL BLOW FROM HIGH TO LOW
The winds would go either North or South except for the Coriolis Effect causes the wind to curve to the
What Global Winds affect
North America?
Prevailing Westerlies
RIGHT

8. Coriolis Effect
The apparent curve of the wind to the right in the Northern Hemisphere.
Caused by Earth’s Rotation
nimations/animation2.html

9. Pressure Systems Surface winds: High = Move OUT of the center
Low = Move IN toward the center
Add the Coriolis effect (curve to the right)
Motion around a High = Clockwise
Motion around a Low = Counter Clockwise
AntiCyclone Cyclone

10. AIR MASSES
Air Mass: A large volume of air defined by its TEMPERATURE and WATER VAPOR.
c = Continental = Dry
m = Maritime = Moist
P = Polar = Cold
T = Tropical = Warm
cP = Continental Polar air =
mP = Maritime Polar air =
cT = Continental Tropical =
mT = Maritime Tropical =
Cold, Dry air from Canada
Cold, Moist air from N. Atlantic
Warm, Dry air from Mexico
Warm, Moist air from Gulf of Mexico

11. Frontal Boundaries
Frontal Boundary = Where two different air masses collide.
Cool, Dry air collides with Warm, Moist air.

12. Cold Front
Cold Front = Where a cP air mass collides with a mT air mass.
cP air is doing the pushing.
mT air is rising UP creating vertical clouds.
Cumulonimbus clouds
Thunderstorm
What is the weather at A?
What is the weather at B?
What is the weather at C? C B A

13. Warm Front
Warm Front = When a mT air mass collides with a cP air mass.
mT air mass is doing the pushing.
As mT air pushes, it rises over the cP air creating low horizontal clouds.
Stratus, nimbostratus, cirrus
What is the weather at A?
What is the weather at B?
What is the weather at C? A C B

14. Weather Map Symbols cP mT
Identify the weather map symbols to determine weather in your area.
Cold Front =
Warm Front = cP mT

15. Weather Forecasting cP NW mT SW

16. Current U.S. Weather Map
May 24, 2011

17. Friday’s Weather Map mP mT

18. Mid-Latitude Cyclone

19. Hurricanes 3 things needed to form a hurricane Low Pressure
Warm ocean temperatures
High humidity

20. Hurricane Where are hurricanes located when at their strongest?
Winds over 76 mph

21. Hurricanes
What happens when the hurricane hits land?

22. Weather Station Model
Used to deliver a lot of information in a small space

23. Weather Map