Wind Lesson

Is Harrisonburg,
VA a good location
for wind energy?
Wind Notes:
• 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
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
• Wind speed is
measured using an
• 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
• 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.
• 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 air
High 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
• 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
• 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.
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
• This is what causes the
Westerlies to curve and flow
WEST to EAST. Otherwise the
wind would flow directly south to
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
Summary of Global Winds
Label them in your notes