Download Global Winds

What is Wind?
 Winds are caused by differences in air
pressure.
 This is horizontal movement of air of high
pressure to low pressure.
 Unequal heating of the atmosphere.
Measuring Wind
 Wind direction is determined by a wind
vane.
 The name of a wind tells where the wind is
coming from. Ex: A north wind comes
from the north blowing south.
Measuring Wind
 Wind speed is measured with a
anemometer.
 The device has usually 3 to 4 cups
mounted at the end of spokes that spin on
an axis.
 The force of the wind against the cups
causes the axis to move.
 A meter on the axle shows the wind speed.
Wind-Chill Factor
 Wind blowing over your skin removes body
heat.
 The stronger the wind the colder you feel.
 The increased cooling of a wind is what we
call the wind-chill factor.
Local Wind
 Local winds are winds that blow over a
short distance.
 Local winds are caused by the unequal
heating of Earth’s surface within a small
area.
Local winds
 Sea Breeze
 Land Breeze
Local Winds
Sea Breezes
 It takes more energy to warm up a large
body of water than the same area of land.
 Heat rises from land, expands creating a
low pressure, then cooler air from the
body of water moves beneath the warm
air.
 This causes the sea breezes during the
daylight hours.
www.prh.noaa.gov/hnl/kids/seabreeze.gif
Land Breezes
 Process is reversed at night.
 Land cools more quickly than water.
 Water warmed during the day expands and
rises, cooler air over land moves beneath
it.
 This creates land breezes moving back
toward the body of water.
Global Winds
 Key point – Like local winds and global
winds are effected by the unequal heating
of Earth’s surface. The difference is that
global winds occur over a large area.
Global Winds
Global Winds
 How it all begins.
 Warm air rises at the equator and cold air
sinks at the poles.
 Air pressure is lower at the equator and
higher near the poles.
Global Winds
 The difference in pressure causes wind
from the poles to blow towards equator.
 However, higher in the atmosphere, air
flows from the equator towards the poles.
 These currents creates global winds.
The Coriolis Effect
 If the Earth did not spin, global winds
would blow in a straight line from the
poles to the equator.
 Earth rotates from East to West
 This curves the winds.
The Coriolis Effect
 The curving of the winds through the
rotation of the Earth is called the Coriolis
Effect.
 Global winds in the Northern Hemisphere
turn right.
 Global winds in the Southern Hemisphere
turn left.
Global Wind Belts
 There are areas of the globe that are
areas of calm.
 These are called the Doldrums and Horse
Latitudes.
Global Wind Belts
 Doldrums are found near the equator
where air rises rapidly but does not move
far horizontally.
 Winds near the equator are very weak or
none at all.
Global Wind Belts
 Horse Latitudes were named for an area
where at 30⁰ N and 30⁰S latitude sailors
reached an area where air stops moving
towards the poles and sinks.
 This created an area with virtually no
winds and sailors ran out of food and
water for their horses and had to throw
the horses overboard.
Global Wind Belts
 Trade Winds
 Prevailing Winds
 Prevailing Easterlies
Global Wind Belts
 Trade winds occur between 30⁰ latitude to
the equator.
 High pressure builds near Horse latitudes
blowing surface winds back towards the
equator.
 In Northern Hemisphere the Coriolis Effect
turns the winds west. Therefore, the winds
are blowing from the Northeast to the
Southwest.
Global Wind Belts
 Prevailing Westerlies occur between 30⁰
and 60⁰ latitude north and south.
 The Coriolis Effect turns the winds toward
the east.
 In the Northern Hemisphere the winds
blow from the Southwest and in the
Southern Hemisphere from the Northwest.
Global Wind Belts
 Cold air near the poles sinks and flows
back towards lower latitudes.
 The Coriolis Effect shifts the polar winds
west, producing the Polar Easterlies.
 These winds have a great effect on our
weather in North America.
Jet Streams
 Above 10 kilometers above Earth’s surface
are bands of high-speed winds called jet
streams.
 Jet streams generally blow from west to
east at speeds of 200 to 400 kilometers
per hour.
 These are the polar and subtropical jet
streams.
 These jet streams move in waves up and
down depending on the time of the year.