The Atmosphere has Wind Patterns.

Wind Wind is the motion of air. It is caused by the uneven heating of Earth’s surface. Air moves from areas of high density to areas of low density. Density can be measured through atmospheric pressure. Wind direction is measured with a wind vane and wind speed is measured with an anemometer.

There are 3 forces that affect the way wind blows The Pressure Gradient Force The pressure gradient force tries to equalize the pressure differences. This causes high pressures to push air toward low pressures. If wind was under the effect of the pressure gradient force only, it would flow directly from high pressure regions to low pressure regions.

The Coriolis Effect The Coriolis Force is caused by Earth’s Rotation. Global winds curve as Earth turns beneath them. Winds in the Northern Hemisphere turn away from the equator in a clockwise direction. Winds in the Southern Hemisphere turn away from the equator in a counter-clockwise direction.

Friction The rough surface of Earth slows down the wind. Question: Where would you expect stronger winds, The Tri-Cities or Seattle?

How Does Earth’s Rotation Affect Wind? Blow up a Balloon. Have a partner slowly rotate the balloon to the right. Draw a line straight down from the top of the balloon to the center of the balloon as it rotates. Now draw a straight line up from the bottom of the balloon straight up to the center as the balloon rotates.

What do You Think? How did the rotation affect the lines? How does this activity demonstrate the Coriolis Effect? How might changing the speed of the balloon’s rotation affect your results? Test your prediction.

Pressure Gradient Force On the diagram use arrows to indicate the direction of air flow due to the pressure gradient force.

PGF + Coriolis Force (Effect) On the diagram use arrows to indicate the direction of air flow due to the Pressure Gradient force and the Coriolis force.

PGF + Coriolis Force + Friction Now combine the three forces to indicate wind direction.

Low Pressure Center Winds converge (come together) in low pressure regions as air is pushed away from high pressure regions. The air in the center must go somewhere, so when air converges near a low, it is forced upward. As the air cools, it cannot hold water vapor. This vapor condenses, which forms clouds and precipitation. Rain, sleet, hail, and snow often take place near low pressure areas.

High Pressure Center When air diverges (moves away from) high pressure areas, the air above sinks to fill the empty space. The sinking air warms. As the air warms, it can hold more water vapor. The clouds will evaporate. Due to this, high pressure areas are usually dry.