 Wind is the horizontal movement of air from an area of high pressure to an area of lower pressure.

Because air is fluid, it can move easily from place to place. Differences in air pressure cause the air to move. These differences in air pressure are caused by the unequal heating of the atmosphere.

Convection currents form when an area of Earth’s surface is heated by the sun’s rays. How would this effect winds?

Air expands over heated surfaces and becomes less dense, causing its air pressure to decrease. In a nearby area that is not heated as much, the air is cooler, denser and has higher air pressure.

The cool, dense air with higher pressure flows underneath the warm, less dense air forcing the warm air to rise. Winds are described by their direction and speed.  Wind vanes determine wind direction. The name of the wind indicates where it’s coming from.

 Wind speed is measured with an anemometer.

 The increased cooling a wind can cause is called the wind- chill factor.  If the temperature outside is 20 degrees Fahrenheit with a wind speed of 30 miles per hour, the wind-chill makes it feel like 1 degree.

Challenge  Make an anemometer. MATERIALS: 5 3-ounce Paper Cups 2 Straight Plastic Soda Straws 1 Straight Pin or Push Pin 1 Sharp Pencil With An Eraser Safety Scissors Paper Hole Punch Small Stapler Ruler

Local Winds  Local winds blow over short distances.  They are caused by the unequal heating of Earth’s surface within a small area.  Local winds only form when large-scale winds are weak.

Sea Breeze  Occurs along the shore of a large body of water.  More energy is needed to warm up this water than an equal area of land.  This results in air over land becoming warmer than the air over water.

Global Winds Global winds blow steadily from specific directions over long distances. They are created by the unequal heating of Earth’s surface and occur over a large area. How does the sun’s rays strike Earth?

Where is the temperature the warmest? The lowest?

Temperature differences between the equator and the poles produce giant convection currents in the atmosphere. Warm air, with less density and pressure, rises at the equator and cold air, higher pressure, sinks at the poles.

This pressure difference causes winds to blow from the poles toward the equator at Earth’s surface. However, air flows away from the equator toward the poles higher up in the atmosphere

The Coriolis Effect The way Earth rotates causes the winds to curve. Because of the Coriolis effect, global winds in the Northern Hemisphere gradually turn toward the right.

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