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WINDS
Understand the cause of wind and
how they affect climate
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Chapter 4
Pages 59-67
What is Wind?
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A wind is a horizontal movement of air
across a surface.
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Vertical movements are currents or updrafts
and downdrafts
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Caused by what????
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Heat versus cold!! Relate it to convection
cells previously studied!!!
What causes wind?
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Unequal heating
Unequal heating causes pressure
differences
Cold, heavy air sinks = high pressure
Warm, expanding air rises = low
pressure
Winds blow from high to low
Know that air blows from areas of high
pressure to areas of low pressure.
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The statement is fact.
Think:
1. Air inside a balloon
2. Exhaling
3. Air powered pellet gun
It is simply fact.
High and low pressures in the earth’s
atmosphere are responsible for wind
P. 59-61
Application - Land Breeze
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Using your knowledge of wind predict & explain
the wind direction below. P. 61
•FACT: Water holds heat
longer than the land.
•During the night, sea
air is warmer than the
air over the land.
•Air rises over sea
Low Pressure
•Relative Low pressure
over sea
•Land air moves to
lower pressure
Land Breeze
Night
time
 Cool
breeze
 Off the
land
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Application - Sea Breeze
►
Using your knowledge of wind predict & explain
the wind direction below. P. 61
•FACT: Land heats up faster
than the water
•During the day, air over the
land is warmer than air over
the sea
•Air rises over land
•Relative Low pressure over
land
•Sea air moves to lower
pressure
•Cold “Breeze” off the ocean
during the day
Low Pressure
Sea Breeze
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Day
time
Cool
Breeze
Off the
ocean
Define the terms wind & prevailing
wind. p.61-63
Wind:
 is a horizontal movement of air across a surface.
 It results from air masses of different temperatures and
humidity lying next to each other.
 The resulting pressure variation causes “wind” to blow
from high pressure areas to low pressure areas.
Prevailing Wind:
 Is regular, predictable, normal wind direction for a
given area or region.
 Caused by global convection cells.
 Named after the direction from which it comes
Prevailing Winds
Describe how the coriolis force
affects wind direction.
Coriolis force =
 objects in motion tend to deflect
 to the right in north hemisphere
 to the left in south hemisphere
Consequently winds:
 in the northern hemisphere tend to curve to the
right of their path.
 while in the southern hemisphere they deflect left
of their path.
Summary of prevailing wind
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Global highs and lows are due to
uneven heating of the earth
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Air moves from high pressure to low
pressure creating winds
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Winds are deflected in the directions
indicated on the diagram due to the
coriolis effect.
Make inferences about how winds are related
to major pressure belts. p.63
 Air rises at the equator
 Low pressures
 It settles at the poles
result where hot
air rises.
 High pressures
result where air
settles
 Result = 6 convection cells
 3 above and 3 below the
equator.
Describe Orographic rainfall p. 66
Leeward
Chinook
Windward
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A relatively warm, moist air blows off the sea
It is forced up by mountains (high relief)
Air cools at higher altitude
Cool air holds less moisture
Consequently clouds condense and rain falls
Most rain falls on the windward side of the relief
Leeward side is often in a dry rain shadow because the
moisture has all been lost
Definitions
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Windward
• The side of the mountain receiving the wind
• (consequently more precipitation as well)
Leeward
• The side of the mountain sheltered from the
wind
• (consequently receives less precipitation)
Rain Shadow
• The area located on the leeward side of a
mountain that receives low amounts of
precipitation.
• Mainly due to the air that descends on the
leeward side has “dumped” on the windward
side.
Describe Frontal rainfall p. 66
•Weather Front2 fronts meet
FRONT
Warm, moist air
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•Hence the
name frontal
rain
Warm Moisture laden air meets cold air
Warm air is less dense & is forced up over the
cooler, more dense air
Warm Moisture laden air cools at higher altitude
Cool air holds less moisture
Consequently clouds condense and rain falls
Describe Convectional rainfall p. 67
•Often
associated
with thunder
storms.
Air heated from the earth
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Usually occurs in hot areas like tropics or continental
summer
Sun heats the earth causing large amounts of water to
evaporate
Hot air rises forming convection currents (hence the name)
Warm Moisture laden air cools at higher altitude
Cool air holds less moisture
Consequently clouds condense and rain falls
Analyze the relationship between wind
systems and temperature.
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1.
2.
3.
4.
How do the
prevailing winds
affect
temperature in:
Argentina
Columbia
Baffin Island
Newfoundland
C
D
B
A
Analyze the relationship between wind
systems and precipitation
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1.
2.
3.
4.
5.
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How do the
prevailing winds
affect
precipitation in:
England
Midwestern U.S.
British Columbia
Northern Africa
Central Australia
Question #26 p.
67 = great active
learning lab
A
C
B
D
E