Local and Global Winds
Wind
• Wind is created by the unequal warming of
the Earth (convection currents)
• Differences in atmospheric pressure cause
the movement of air.
• A low pressure system is formed when hot
air rises. A high pressure system is formed
when cold air falls.
Wind
• There are two types of wind:
–Global
–Local
Local Winds
• Contrary to global winds,
local winds can change
speed and direction
frequently.
• These are the winds that
we feel on the Earth.
• They are created by local
weather and temperature
conditions.
Local Winds
• Sea Breeze
– During the day, the Earth warms faster then
the water. Therefore the breeze blows from
the ocean to the Earth. This is called a Sea
Breeze.
Local Winds
Land Breeze
– During the night, the Earth cools down faster then
the water, which creates a land breeze. The wind
blows from the land to the Ocean.
– Video
• Fill in sheet – land and sea breeze
Global Winds
• They generally blow at the same speed and
direction.
• They are due to the combination of
convection currents and the Coriolis effect
(rotation of the Earth).
• Some are very high in the atmosphere so we
cannot feel them on Earth.
• Each hemisphere contains 3 major wind
systems that divide the global winds.
• The Trade winds, the Prevailing westerlies and the
Polar easterlies
Global Wind Patterns
Main wind currents:
•Polar Easterlies (north
and south)
•Prevailing Westerlies
(north and south)
•Northeast Tradewinds
(north only)
•Southeast Tradewinds
(south only)
Note: ‘prevailing’ means to the
usual direction from which the wind
blows!
See Figure 1.19, page 31
Global Wind Systems
Wind System
Location
•
Trade winds
•
•
Prevailing westerlies •
•
Polar Easterlies
•
Path
Between equator and 30o N
latitude
Between equator and 30o S
latitude
•
Between 30o and 60o N
latitude
Between 30o and 60o S
latitude
• Air circulation pattern is
Between 60o N latitude and
NP
Between 60o S latitude and
SP
• Air circulation pattern is
See Table 1.3, page 31
•
•
•
Air at equator warms, rises
and travels to 30o N or S lat.
At 30o N or S, air cools, sinks
& moves W toward Equator
& deflected W
opposite to that of the trade
winds
Surface winds blow from W to
E and towards Poles
similar to that of the trade
winds
Surface winds blow from E to
W and away from Poles
Global Warming and Cooling of Air
• Air is warmest at the equator
and coolest at poles
• So air should rise at the equator
and sink at the poles
• However, due to the size of the
Earth, air from the equator
cools before it reaches the
poles and air from the poles
will warm before it reaches the
equator
See Figures 1.16.1.17, page
30
Actual Wind Currents
• More
realistically, we
see pockets of
convection
currents above
the Earth’s
surface.
Coriolis Effect
• Due to the rotation of
the Earth, any object
that moves across the
surface of the Earth will
be pushed to the left or
right
• Video
• Video
• In the Northern Hemisphere, the coriolis
effect blows the winds from West to East
(prevailing Westerlies). That’s the reason why
most of our weather systems come from the
West of Canada.
• Video – Atmospheric Circulation
• Notes/practice sheet
Jet Streams
• A narrow band of fastmoving wind
• Between the
troposphere and the
stratosphere
• Aided by the Coriolis
Effect
• Up to 300 kph
• Altitude 10 – 12 km
Polar Jet Streams
• Major jet streams are polar jet
streams
• Separate the polar easterlies
from prevailing westerlies in
NH and SH
• Move west to east
See Figure 1.20, page 32
Subtropical Jet Streams
• Minor jet streams are
subtropical jet streams
• Occur where trade winds
meet westerlies
• Move west to east
• Storms form along jet
streams & cause largescale weather systems
• Weather systems usually
follow the path of jet
streams
See Figure 1.20, page 32
Jet Streams
• The polar jet stream, which mostly affects the
Canadian climate, forms when the Prevailing
westerlies and polar Easterlies meet.
• In general, the weather is colder North of the
jet stream and warmer South of the Jet
stream.
Jet Streams
• What happens to the jet stream when the
seasons change?
– During the winter, the jet stream moves South.
– During the summer, the jet stream moves up to
the North.
• Jet Streams – Video
• Notes
• Practice sheet: Worldwide Wind Currents
Quiz