1. Chapter 19: The Atmosphere in Motion
19.1: Air Pressure and Wind
19.2: Factors Affecting Winds
19.3: Global Wind Patterns
19.4: Continental and Local Winds

2. 19.1: Air Pressure and Wind Air Pressure
Air Pressure- The weight of the atmosphere as it pushes down upon Earth's surface exerts a force per unit of area called air pressure.
Air pressure decreases by about 50% for each 5 km (3 mi) increase in elevation.

3. 19.1: Air Pressure and Wind B. Measuring Air Pressure
Mercury
B. Measuring Air Pressure
A barometer is used to measure air pressure.
Two Types: Mercury and Aneroid. P.414 & 415
Air pressure at sea level is 30 in Hg. Or 1013 millibars.
If air pressure increases the column rises, if it decreases it falls.
Click me
Aneroid

4. 19.1: Air Pressure and Wind Why Does Air Pressure Change?
Elevation, temperature and Humidity all affect air pressure.
This is a result of air molecules being closer or farther apart. Higher elevations mean fewer air molecules. Why? Warmer air causes air molecules to be spaced farther apart and moist air molecules are also spread farther apart.
A decrease in air pressure usually indicates the approach of warm, moist air.
Isobar-a line that joins points of equal pressure.
Answer:
Less Gravitational Pull

5. 19.1: Air Pressure and Wind D. What Makes Wind Blow?
Air moves from areas of high pressure to areas of low pressure. The greater the difference the quicker it moves. This causes WIND!

6. 19.1: Air Pressure and Wind 2. What creates these differences?
3. Meteorologists use a wind vane to measure direction and an anemometer to measure speed.
Answer:
Differences in Pressure, Temperature, and Altitude

7. 19.2: Factors Affecting Winds
If the earth were perfectly smooth and did not rotate, air would flow straight from high-pressure areas to low pressure areas.

8. 19.2: Factors Affecting Winds
The Coriolis Effect
It is the tendency of an object moving freely over the Earth's surface to curve away from its path of travel. See page 419.
In the Northern Hemisphere objects are deflected to their right and in the Southern Hemisphere the objects are deflected to the left.
Coriolis Effect

9. 19.2: Factors Affecting Winds
B. Friction
The smoother the surface the faster the wind!
Jet Stream- Bands of swiftly moving winds formed in the troposphere.
Polar Jet Stream- Cool air from polar regions combines with warmer air to the south.

10. 19.3: Global Wind Patterns
Factors that affect winds are: Temperature differences between equatorial and polar regions, the rotation of the earth, locations of the continents, the time of year and local topography.

11. 19.3: Global Wind Patterns Effects of Earth's Rotation
Three Celled Circulation Model- The Northern and Southern hemispheres each have three circulation cells: one between the equator and 30° lat., the second between 30° and 60° lat., and a third between 60° lat. and the pole. See page 423.

12. 19.3: Global Wind Patterns
2. The circulation cells are caused by alternating bands of high and low pressure.
3. There are weaknesses in the Three-Celled Model. These can be attributed to generalizations about the earth landscape and seasons.

13. 19.3: Global Wind Patterns Description of Wind and Pressure Belts
Intertropical Convergence Zone- The air is hot and humid, there is little wind, and rain is common. This area is historically called the doldrums.
Horse Latitudes- Found between latitudes of 20°-30°. They are created by dry sinking air, which creates little wind and precipitation.

14. 19.3: Global Wind Patterns
3. Trade Winds- Found between the doldrums and the horse latitudes. They are warm and relatively steady in both direction and speed.
4. Prevailing winds- Blow from the same direction.

15. 19.4: Continental and Local Winds
Winds change with the changing of the seasons due to changes in temperatures.

16. 19.4: Continental and Local Winds
Effects of Seasons and Continents
Air pressure on continents is low in the summer and high in the winter. The opposite is true for the oceans. See page 427.
Monsoons-Winds that change direction seasonally.
Summer
moist
moist H H
Warm
Hot
Warm

17. 19.4: Continental and Local Winds
Land and Sea Breezes
Hot
Cooler H L
Cool
Warm
LAND-BREEZE
SEA-BREEZE