Download The Causes of Weather

UNIT 1 Chapter 1: Inquiring about Weather
Section 1.2
1.2 The Causes of Weather
The amount of solar energy that Earth receives every year is
the same amount that Earth radiates back into space. The
distribution of this energy is not equal throughout Earth. Three
factors affect the distribution of solar energy on Earth.
• Earth’s curved surface
• Earth’s tilt on its axis
• Earth’s orbit
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UNIT 1 Chapter 1: Inquiring about Weather
Section 1.2
How Earth’s Curved Surface Affects Weather
• The amount of solar energy that reaches different regions of Earth varies
because of Earth’s curved surface.
• The concentration of light that warms Earth’s surface is unequally
distributed.
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UNIT 1 Chapter 1: Inquiring about Weather
Section 1.2
How Earth’s Tilt Affects Weather
• Earth’s tilt causes the yearly pattern of changes called
seasons.
• As Earth orbits the Sun, the northern hemisphere is
sometimes tilted toward the Sun and at other times it is
tilted away.
• Show Animation
Describe how the tilt of the
Earth affects temperatures
in the Northern
Hemisphere.
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How Earth’s Tilt Affects Weather
Describe how the tilt of the Earth affects temperatures in the
Northern Hemisphere.
When the earth is tilted towards the sun solar energy strikes the
region more directly resulting in warmer temperatures
(summer) when tilted away the opposite is true so it will be
colder temperatures (winter).
UNIT 1 Chapter 1: Inquiring about Weather
Section 1.2
How Earth’s Orbit Affects Weather
• The shape of Earth’s orbit affects how
much solar energy it receives.
• When Earth’s orbit is more oval, Earth
gets much more solar energy when it is
nearest the Sun than when it is farthest
from the Sun.
• When the orbit is circular, solar energy is
more evenly balanced during the year.
• How long does it take Earth to cycle from
an oval orbit to a circular orbit?
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How Earth’s Orbit Affects Weather
• How long does it take Earth to cycle from an oval orbit to a
circular orbit?
It takes about 100 000 years to complete Earth’s orbit changes
from being more circular to being more oval and back again to
being more circular.
Therefore the impact of orbit on the weather you experience dayto-day would be minimal compared to curvature and tilt of the
earth.
UNIT 1 Chapter 1: Inquiring about Weather
Air Masses
• The air over a warm surface can
be heated, causing it to rise
above more dense air.
• The result is the formation of an
air mass—a very large mass of
air that has the same properties,
such as humidity and
temperature, as the area over
which the air mass forms.
• Which air mass is shown nearest Nova
Scotia, and what are the characteristics
of it?
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Section 1.2
Air Masses
• Which air mass is shown nearest Nova Scotia, and what are
the characteristics of it?
• The maritime polar (Atlantic) air masses are closest to Nova
Scotia.
• These bring cold and humid winters.
• Also cool and humid summers.
• What are key words for arctic, polar, tropical?
• What are key words for continental and maritime?
UNIT 1 Chapter 1: Inquiring about Weather
Air Masses
What other air masses
can you see? How do
they affect other parts of
North America?
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Section 1.2
UNIT 1 Chapter 1: Inquiring about Weather
High Pressure Systems
• When an air mass cools over an
ocean or a cold region of land, a
high pressure system forms.
• As the air mass cools, the air
mass becomes more dense.
• When the air mass contracts, it
draws in surrounding air from the
upper atmosphere.
How does wind form in this
process?
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Section 1.2
High Pressure Systems
How does wind form in this process?
The added weight increases atmospheric pressure. The dense,
high pressure air moves outward toward areas of lower
pressure.
This movement of air from an area of high pressure to an area of
low pressure is what people often refer to as wind.
What type of weather is usually associated with high pressure?
High Pressure Systems
What type of weather is usually associated with high pressure?
High pressure systems often bring clear skies.
UNIT 1 Chapter 1: Inquiring about Weather
Low Pressure Systems
• Air masses that travel over warm land or
oceans may develop into low pressure
systems.
• When an air mass warms, it expands and
rises. As it rises, it cools.
• Water vapour in the air may condense,
producing clouds or precipitation.
What kind of weather is expected
when there is a low pressure system?
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Section 1.2
Low Pressure Systems
What kind of weather is expected when there is a low pressure
system?
When an air mass warms, it expands and rises, making the layer
of air thicker. However, as the air rises, it cools. Water vapour
in the air may condense, producing clouds or precipitation.
This is why low pressure systems often bring wet weather.
Compare High and Low Pressure systems
page 29
High Pressure System
Low Pressure System
air descending
air rising
more pressure below
leaving less-dense air below
Northern Hemisphere air flow curve
results in clockwise rotation
Northern Hemisphere air flow results
in counter clockwise direction
(opposite for Southern Hemisphere)
(opposite for Southern Hemisphere)
Check Your Understanding page 32
9. Earth’s curvature, tilt and orbit
10. An air mass is a very large mass of air that has the same
properties, such as humidity and temperature, as the area over
which it forms.
The five major types of air masses are: Arctic; continental
polar; continental tropical; maritime polar and maritime
tropical.
11. In high and low pressure systems, movement of air from an
area of higher pressure to an area of lower pressure results in
wind.
12. The Coriolis effect.
UNIT 1 Chapter 1: Inquiring about Weather
The Coriolis Effect and Wind
• The Coriolis effect is a change in
the direction of moving air, water,
or any objects on Earth’s surface
due to Earth’s rotation.
• As Earth rotates, any location at
the equator travels much faster
than a location near either of the
poles.
Show Animation
Section 1.2
The Coriolis Effect and Wind
Explain in your own words why the actual
path of wind is curved in the northern and
southern hemispheres.
Due to the earth’s rotation any
location at the equator travels much faster
than a location near either of the poles. Air
rising from the equator travels east quickly
in the same direction that the Earth rotates.
As a result, the Coriolis effect deflects
winds to the right in the northern
hemisphere and to the left in the southern
hemisphere.
UNIT 1 Chapter 1: Inquiring about Weather
Section 1.2
Global Wind Systems
Wind systems are wide zones of
prevailing winds. There are three
major wind systems, which occur
in both hemispheres.
•Trade Winds
•Prevailing Westerlies
•Polar Easterlies
•Explanation on Global Wind
Systems U-tube video
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How does the air circulation of the trade winds
compare with the air circulation of the prevailing
westerlies?
Global Wind Systems
How does the air circulation of the
trade winds compare with the air
circulation of the prevailing
westerlies?
The Trade winds move east to west
and move toward the equator.
The Westerlies move west to east and
toward the Poles.
UNIT 1 Chapter 1: Inquiring about Weather
Section 1.2
Jet Streams
A large temperature gradient in upper-level air, combined with
the Coriolis effect, results in strong westerly winds called jet
streams.
•A jet stream is a narrow band of fast-moving wind.
•A jet stream can have a speed up to 300 km/h or greater at
altitudes of 10 km to 12 km.
•Storms form along jet streams and
generate large-scale weather systems.
•Video of jet stream
•What do the jet stream and seasons
have in common?
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Jet Streams
•What do the jet stream and seasons
have in common?
-position of the jet stream varies with
the seasons.
-generally located in the region of the
strongest temperature differences
- can move almost due south or north
instead of following its normal eastto-west flow.
Jet Streams and Storms
Storms form along jet streams and
generate large-scale weather systems.
These systems transport cold surface
air towards the tropics and warm
surface air toward the poles.
Weather systems generally follow the
path of jet streams.
Jet streams also affect the intensity of
weather systems by moving air at
different temperatures from one
region of earth to another.
UNIT 1 Chapter 1: Inquiring about Weather
Section 1.2
Fronts
A front is a zone that develops as a result of the meeting of
two air masses with different characteristics.
•Each air mass has its own temperature and pressure.
•An approaching front means a change in the weather, and the
extent of the change depends on the difference between
conditions in the air masses.
•Fronts usually bring precipitation.
•Animation on fronts
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Continued…
UNIT 1 Chapter 1: Inquiring about Weather
Fronts
Why does an
approaching front
signal a change in
weather?
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Section 1.2
Why does an approaching front signal a change
in weather?
When a front moves through an area, the atmospheric conditions
change and these changed conditions cause the weather to
change.
UNIT 1 Chapter 1: Inquiring about Weather
Section 1.2
Extreme Weather
• Thunderstorms are extreme weather events that include
lightning, thunder, strong winds, and hail or rain.
• A tornado is a violent, funnel-shaped column of rotating air
that touches the ground.
• When tornados form over
water, waterspouts occur.
• What causes a thunderstorm?
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Continued…
What causes a thunderstorm?
Thunderstorms occur when water vapour in rising warm air
condenses, releasing thermal energy.
The energy further heats the air, which continues to rise.
The condensation produces large thunderheads, which can
produce extremely heavy rain and hail.
Video of thunderstorm
UNIT 1 Chapter 1: Inquiring about Weather
Section 1.2
Extreme Weather
When strong horizontal winds hit the rapidly rising air in a thunderhead, funnel clouds can result.
Strong winds tilt the funnel cloud (A). The funnel cloud becomes vertical and touches the ground (B). A
tornado forms as the funnel cloud travels along the ground. (C).
What characteristic of a tornado makes it so dangerous?
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Continued…
What characteristic of a tornado makes it so
dangerous?
The high winds of tornadoes can tear homes into pieces, lift roofs
off of buildings, and fill the air with fast moving projectiles
that kill people and other living things.
Video on tornadoes
UNIT 1 Chapter 1: Inquiring about Weather
Section 1.2
Extreme Weather
• The tropics, the regions closest to the equator, are the ideal
location for the formation of intense storms called tropical
cyclones to occur.
• Wind speeds of tropical cyclones may reach 240 km/h.
• Tropical cyclones are also called cyclones, typhoons, or
hurricanes.
• Hurricane season extends from late summer to early fall.
What is the difference between a typhoon and hurricane?
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UNIT 1 Chapter 1: Inquiring about Weather
Extreme Weather
This is a cross-section of a hurricane (A) and a satellite
image of a hurricane (B).
Why do tropical cyclones originate in the tropics?
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Section 1.2
Why do tropical cyclones originate in the
tropics?
The warm waters in the tropical regions contain a lot of thermal
energy that can fuel the storm.
Video of hurricane
Video of cyclone
Video of typhoon
UNIT 1 Chapter 1: Inquiring about Weather
Section 1.2
Section 1.2 Review
• Earth’s shape, tilt, and orbit affect weather.
• Five main air masses affect North America. The cooling
and warming of air masses creates high and low pressure
systems, respectively. Fronts form where two air masses
meet.
• The Coriolis effect and differences in atmospheric pressure
create global wind systems.
• Rapidly rising warm air results in extreme weather such as
tropical cyclones, thunderstorms, and tornadoes.
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Section Review page 39
Know the answers to the following questions:
#1,2,3,4,5,6,7,8,9,10,11,12 (1-12) 15,16
Chapter Review
Know the answers to the following questions:
#1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,17,19,20,21,23
,27,28