1. Understanding Air Pressure

2. Air Pressure Is exerted in all directions: down, up, sideways
Sea level pressure = 1 kilogram per square inch.

3. Measuring Air Pressure
Barometer – used to tell the air pressure around you (in millibars)
Increase in AP = Mercury rises
Decrease in AP = Mercury lowers

4. Wind A result of horizontal differences in air pressure.
Flows from high to low pressure
Solar radiation = ultimate source for wind.

5. Control Wind Three factors: 1.) Pressure Differences
2.) Coriolis Effect
3.) Friction

6. Pressure Differences Pressure Gradient – read from isobars
Close isobars = high winds
Far apart isobars = low winds

7. Coriolis Effect 1.) A right angle to the direction of air flow
2.) Affects wind direction and wind speed.
3.) Strong wind = strong deflection
4.) Strong at poles and weak at equator

8. Friction Slows down air movement which changes direction.
Above layer = parallel to isobars (low friction)
Jet streams = fast moving “rivers” of air

9. Pressure Centers and Wind
Fancy for: Cyclones

10. High Pressure vs. Low Pressure
Anticyclones
Pressure increases from outside to center
Winds blow outward and clockwise
Net flow = outward
Cyclones
Pressure decreases from outer to center
Winds blow inward and counterclockwise
Net Flow = inward

11. Weather and Air Pressure
Rising air = cloud formation and precipitation.
Sinking air = clear skies
Have to have convergence and divergence!

12. Weather Forecasting
Low pressure system = bad weather!

13. Global Winds Atmosphere = Air conditioner
Warm air goes toward high latitudes
Cool air towards equator.

14. Non – Rotating Earth Model
Where hot air goes to the poles when it reaches the troposphere.

15. Rotating Earth Model 4 pockets: 1.) Trade Winds 2.) Westerlies
3.) Polar Easterlies
4.) Polar Front

16. Influence of Continents
Southern Hemisphere = continuous pressure system.
Land + Water = different pressure systems

17. Monsoons
Seasonal changes in the wind direction.
LOTS OF RAIN!!!

18. Regional Wind Systems
Section 19.3

19. General Info
Circulation in the middle latitudes is complex and does not fit the convection system described for the tropics.

20. Local Winds
Caused by either topographic effect or by variations in surface composition.
Land and Water

21. Valley and Mountain Breezes
Valley Breeze – heat during the day = warm air that rises
Mountain Breeze – cooling at night = air moving into the valley

22. Measuring Wind Two basic measurements
Direction and Speed
Labeled by the direction they flow
Ex. North wind – north towards the south
Measured by a wind vane

23. Wind Direction Wind Speed
Prevailing wind – blows fro the same direction consistently
Ex. Westerlies (US)
Wind Speed
Measured by an anemometer

24. El Nino
Warm countercurrents that become unusually strong and replace cold offshore water with warm water.
3 – 7 years

25. La Nina
When surface temperatures in the eastern Pacific are colder than average
Distinctive set of weather patterns.