WIND
What causes wind?
 All winds are caused by differences in
air pressure.
 Wind is the horizontal movement of air
from an area of high pressure to an area
of low pressure.
 Differences in air pressure is caused by
unequal heating of the atmosphere.
Measuring Wind
 South winds blow from the south
toward the north. North winds blow
from the north toward the south.
 An anemometer measures wind speed.
 An example of wind chill factor is if it
is 20 F and the wind speed is 30 mph the
wind chill factor makes it feel like -18 F.
Local Winds
 They blow over a short distance.
 They are caused by unequal heating of
Earth’s surface within a small area.
 They form only when no winds are
blowing from far away.
Sea Breezes
 Occur during the day.
 The land will heat up faster during the
day than the water.
 The cool air blows inland from the
water pushing up the warm air.
 The wind that blows from the water is
known as sea breezes.
Land Breezes
 Occur during the night.
 The land cools off more quickly than
the water.
 Therefore the cool air moves over the
water causing the warmer air to rise.
Global Winds
 They are long distance winds that blow
steadily from specific directions.
 The movement of air between the equator
and the poles produces global winds.
 The Coriolis effect is wind curvature due to
Earth’s rotation.
 If the Earth didn’t rotate, the wind would
blow in a straight line from the poles toward
the equator.
Global Wind Belts
 Major
wind belts
are trade
winds,
prevailing
westerlies,
and polar
easterlies.
Doldrums
 Very little horizontal movement.
 Region near equator with little or no
wind.
Horse Latitude
 30 degrees N latitude
 30 degrees S latitude
Trade Winds
 Winds in the Northern hemisphere between
30 degrees N latitude and the equator blow
generally from the northeast.
 Winds in the southern hemisphere between 30
degrees S latitude and the equator blow
generally from the southeast.
 Hundreds of years ago, sailors relied on the
trade winds to carry cargo from Europe to
the West Indies and South America.
Prevailing Westerlies
 They blow generally from the Southwest
between 30 degrees N and 60 degrees N
latitude.
 They blow from the northwest between
30 degrees S and 60 degrees S latitude.
 They play an important role in the
weather of the United States.
Polar Easterlies
 The coriolis effect shifts polar winds to
the west.
 They meet the prevailing westerlies at
about 60 degrees N and 60 degrees S
latitude.
Jet Streams
 10 km above the earth’s surface are
bands of high-speed winds.
 They blow from the west to the east at
speeds of 200-400km/h.
 Airplanes are aided by the jet stream
when traveling east.
 Airplanes flying at jet stream altitudes
are slowed down when traveling west
against the jet stream winds.