1. Global Winds and Local Winds
What is Wind?
The movement of air caused by air pressure is called wind.

2. What Causes Differences in Air Pressure?
Blue arrows = cool air
Red arrows = warm air
Difference in air pressure are generally caused by the unequal heating of the earth.
The equator receives more direct solar energy than other latitudes, so the equator is warmer and less dense.
Warm, less dense air rises and creates an area of low pressure.
The warm air flows toward the poles.
At the poles, the air is colder and denser, so it sinks.
As the cold air sinks, it creates areas of high pressure around the poles.
This cold air then flows toward the equator.

3. Pressure Belts are found at every 30º
Air travels in many large, circular patterns called convection cells.
Convection cells are separated by pressure belts, bands of high pressure and low pressure found at every 30º of latitude.
Sinking air causes areas
of high pressure because
sinking air presses down
on the air beneath it.

4. The Coriolis Effect and Global Winds
Because of the Coriolis Effect in the Northern hemisphere, winds traveling north curve to the east, and winds traveling south curve to the west.

5. Convection cells found every 30º of latitude and the Coriolis Effect → Global Winds
Westerlies
Located between 30º and 60º latitude in both hemispheres
Flow toward the poles from west to east
In the US, produce rain and snow
Polar Easterlies
Located from the poles to 60º latitude in both hemispheres
Formed as cold, sinking air moves from the poles toward 60º north and 60º south latitude.
In the US, they produce snow and freezing weather

6. Global Winds Continued
Trade Winds
Located from 30º latitude almost to the equator
The Coriolis Effect causes these to curve
How do they get their name?
Early traders would use these winds to sail from Europe to the Americas.

7. Global Winds Continued
The Doldrums
Located in an area around the equator
There is very little wind because the warm, rising air creates an area of low pressure
The name doldrums means “dull” or “sluggish”
The Horse Latitudes
Located 30º north and 30º south latitude
The winds here are weak
The name was given to these areas when sailing ships carried horses from Europe to the Americas. When the ships were stuck in a windless area, the horses were sometimes thrown overboard to save drinking water for the sailors.
Most of the world’s deserts are located in the horse latitudes because the sinking air is very dry.

8. Jet Streams
Jet Streams are narrow belts of high- speed winds that blow the upper troposphere and lower stratosphere.
They can reach maximum speeds of 400 km/h
They do not follow regular paths around the earth like other global winds.
Pilots use these to fly somewhere faster
Meteorologists use these to track the movement of storms

9. Local Winds
Local winds generally move short distances and can blow from any direction.
A shoreline or a mountain can produce temperature differences that cause local winds.
Mountain and Valley Breezes
The sun warms the air along the mountain slopes. This warm air rises up the mountain slopes, creating a valley breeze.
At night, the air along the mountain slopes cools. This cool air moves down the slopes into the valleys, producing a mountain breeze.

10. Land and Sea Breezes