Wind

Is Harrisonburg, VA a good location for wind energy?

• Air moves from areas of HIGH pressure to areas of LOW pressure.

• This movement of the air is the wind

Example: When you blow up a balloon, you increase the air pressure inside the balloon. When you let go of the end, the air rushes out of the balloon

Wind Notes:

What causes differences in air pressure?

• Differences in air pressure are caused by UNEVEN HEATING of the Earth’s surface by the sun.

• Therefore, the sun and solar energy is the ultimate cause of the wind.

Measuring Wind Speed and Direction

• Wind speed is measured using an anemometer

• Wind direction is measured with a wind vane

Local Winds• The land heats and cools faster than the

sea. Water retains heat longer than land, and also takes longer to heat and cool.

• This causes temperature differences between the land and the sea, which leads to a thermal circulation (or wind based on temperature differences).

• During the day, the land heats up faster, the hot air rises, creating an area of lower pressure. Wind blows from the sea to the land. This is a sea breeze.

• At night, the land cools off faster than the sea. Cooler air descends creating an area of higher pressure. Wind blows from the land to the sea. This is a land breeze.

Global Winds• A. The uneven heating of the surface of

Earth causes differences in DENSITY in the air, which results in CONVECTION CURRENTS in our atmosphere.

Convection Current

• B. As the warm, moist air rises, it creates a zone of low pressure, clouds, and precipitation along the equator.  As that warm air rises, it eventually reaches the

stratosphere and can rise no higher.  It spreads outwards towards the poles.

• C. As it spreads, it cools and sinks back down to the surface at about 30°north and south of the equator.  This sinking air produces areas of higher pressure with drier conditions.

30 degrees- sinking airHigh Pressure

Deserts form here:Sahara Desert

• D. Some of this air, as it sinks, moves back towards the equator. This air flowing back towards the equator produces what are known as the trade winds.

• E. The area near the equator where these winds die out is referred to as the doldrums.

Trade Winds

Doldrums

• F. Winds traveling along the surface of the earth from 30 - 60 degrees north and south of the equator are called WESTERLIES. They flow from the west to the east and the original northward wind becomes curved due to the CORIOLIS EFFECT.

Westerlies

• G. The air currents moving along the surface of Earth from the poles 90° to 60° north and south of the equator, flow from east to west and are referred to as the polar easterlies.

Easterlies

Coriolis Effect• Because of the Earth's rotation,

any freely moving object or fluid will appear to:

• Turn to the right of its direction of motion in the Northern Hemisphere and

• Turn to the left of its direction of motion in the Southern Hemisphere.

• This is what causes the Westerlies to curve and flow WEST to EAST. Otherwise the wind would flow directly south to north.

Also about the Coriolis Effect……• This causes winds to travel

clockwise around high pressure systems in the Northern Hemisphere, and counter-clockwise in the Southern Hemisphere.

Low pressure winds travel in the opposite direction (counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere).

Summary of Global WindsLabel them in your notes