Download Unit 2: Weather Dynamics Section 1.2: The Causes of Weather

UNIT 2
Chapter 1: Inquiring about Weather
Unit 2: Weather Dynamics
Section 1.2: The Causes of Weather
Science 10
Mrs. Purba
UNIT 2 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.
1. Earth’s curved surface
2. Earth’s tilt on its axis
3. Earth’s orbit
UNIT 2 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.
UNIT 2 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.
Describe how the tilt of the
Earth affects temperatures
in the Northern
Hemisphere.
UNIT 2 Chapter 1: Inquiring about Weather
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?
Section 1.2
UNIT 2 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?
Section 1.2
UNIT 2 Chapter 1: Inquiring about Weather
Air Masses
What other air masses
can you see? How do they
affect other parts of North
America?
Section 1.2
UNIT 2 Chapter 1: Inquiring about Weather
Section 1.2
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.
• Earth's rotation causes wind to travel
in a clockwise direction around a
high pressure centre (H).
How does wind form in this process?
UNIT 2 Chapter 1: Inquiring about Weather
Section 1.2
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.
• Earth's rotation causes wind to travel
in a counterclockwise direction
around a high pressure centre (L).
What kind of weather is
expected when there is a low
pressure system?
UNIT 2 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.
Explain in your own words why the
actual path of wind is curved in the
northern and southern hemispheres.
Section 1.2
UNIT 2 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
How does the air circulation of the trade winds
compare with the air circulation of the prevailing
westerlies?
UNIT 2 Chapter 1: Inquiring about Weather
Global Wind Systems
Section 1.2
UNIT 2 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.
What do the jet stream and seasons
have in common?
UNIT 2 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.
UNIT 2 Chapter 1: Inquiring about Weather
Fronts
Why does an
approaching front signal a
change in weather?
Section 1.2
UNIT 2 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?
UNIT 2 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?
UNIT 2 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 (the period
when the oceans store the greatest amount of thermal energy).
UNIT 2 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?
Section 1.2
UNIT 2 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.