1. Wind Currents Air Pressure

2. The uneven heating of Earth’s Surface cause differences in air pressure. The force exerted by the air is called air pressure Air Pressure is measured with a barometer The higher the air pressure the more force is exerted on the mercury and it is forced up in the tube.

3. Low Pressure Areas Warm air expands, and is therefore less Dense, warm air rises leaving an area of low pressure Warm air often contains moisture The air cools in the upper atmosphere and the moister forms clouds and rain Low pressure areas tend to be cloudy and rainy Persistent low pressure areas can be found at the equator 0 0 and 60 0 N+S Latitude

4. High Pressure Areas High pressure is caused by cool, dry air sinking (Remember it lost the moisture over the low pressure area.) Cooler air is more dense High pressure areas tend to be clear, sunny and dry, little wind and no rain. Persistent high pressure areas exist at 30 0 N+S and at the Poles 90 0

5. What causes Wind Wind is created when air moves from areas of high pressure to areas of low pressure.

6. Global Wind Patterns