Download Unit 2: Weather Dynamics Chapter 1: Air Masses

UNIT 2
Chapter 1: Inquiring about Weather
Unit 2: Weather Dynamics
Chapter 1: Air Masses
Science 10
Mrs. Purba
Section 1.2
UNIT 2
Chapter 1: Inquiring about Weather
Why do these air balloons rise?
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Warm air rises and cool air sinks. In a hot air
balloon, a heater heats the air inside the
balloon.
When the weight of the warm air plus the
balloon is less than the weight of the cooler
air outside the balloon, the balloon will rise.
Air masses work on the same principles,
rising and falling when they confront an
obstacle, such as another air mass.
Section 1.2
UNIT 2
Chapter 1: Inquiring about Weather
Air Masses
• An air mass is a huge body of air
with similar temperature and
moisture properties.
• The types of air masses formed on
Earth are determined by their
source region.
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
There are four types of air
1. Continental Air - which is air over
a large land mass.
2. Maritime air – which usually
originates over a large water body
and is moist.
3. Tropical Air - which is formed in
region which are usually warm
4. Polar Air – very cold air, usually in
the areas of the polar ice caps.
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
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?
Section 1.2
UNIT 2
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?
Section 1.2
UNIT 2
Chapter 1: Inquiring about Weather
The Coriolis Effect and Wind
• The Coriolis effect describes how
Earth’s rotation steers winds and
surface ocean currents.
• Coriolis causes freely moving objects
to appear to move to the right in the
Northern Hemisphere and to the left
in the Southern Hemisphere.
• The objects themselves are actually
moving straight, but the Earth is
rotating beneath them, so they seem
to bend or curve.
• As wind or an ocean current moves,
the Earth spins underneath it.
Section 1.2
UNIT 2
Chapter 1: Inquiring about Weather
Section 1.2
The Coriolis Effect and Wind
• As a result, an object moving north or
south along the Earth will appear to
move in a curve instead of in a straight
line.
• Wind or water that travels toward the
poles from the equator is deflected to the
east, while wind or water that travels
toward the equator from the poles gets
bent to the west.
• The Coriolis effect bends the direction of
surface currents to the right in the
Northern Hemisphere and left in the
Southern Hemisphere.
Explain in your own words
why the actual path of wind
is curved in the northern
and southern hemispheres.
UNIT 2
Chapter 1: Inquiring about Weather
Spin-offs On A Rotating Sphere
• The ocean and atmosphere are in
constant motion.
• Powered by the Sun and a rotating
Earth, their interactions play a critical
role in shaping weather and climate.
• Natural variations in winds, currents, and
ocean temperatures can temporarily
affect weather patterns.
Section 1.2
UNIT 2
Chapter 1: Inquiring about Weather
Section 1.2
Jet Streams
• A jet stream is a narrow band of fast-moving air that lies between the
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troposphere and the stratosphere.
A jet stream can have a speed up to 300 km/h or greater at altitudes
of 10 km to 12 km.
Jet streams form large temperature differences
between two air masses.
This explains why polar jet streams are powerful,
and why they have turbulent weather.
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
Fronts
• When cold air masses move south from the poles, they run
into warm air masses moving north from the tropics.
• The boundary between two air masses is called a front.
• Air masses usually don’t mix at a front.
• Each air mass has its own temperature and pressure.
• The differences in temperature and pressure
cause clouds and precipitation.
• Types of fronts include cold, warm, occluded,
and stationary fronts.
• 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.
Section 1.2
UNIT 2
Chapter 1: Inquiring about Weather
Section 1.2
Cold Front
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A cold front forms when a cold air mass runs into a warm air mass.
The cold air mass moves faster than the warm air mass.
So the cold air mass lifts the warm air mass out of its way.
As the warm air rises, its water vapour condenses.
Clouds form, and precipitation falls.
If the warm air is very humid,
precipitation can be heavy.
• Temperature and pressure
differences between the
two air masses cause winds.
• Winds may be very strong
along a cold front.
UNIT 2
Chapter 1: Inquiring about Weather
Section 1.2
Cold Front
• Cold fronts often bring sudden changes in the weather.
• There may be a thin line of storms right at the front that moves as
it moves.
• In the spring and summer, the storms may be thunderstorms and
tornadoes.
• In the late fall and winter, the
storms may bring snow.
• A squall line is a bunch of severe
thunderstorms that form near
a cold front.
UNIT 2
Chapter 1: Inquiring about Weather
Warm Front
• When a warm air mass runs into a cold air mass, it creates a
warm front.
• The warm air mass is moving faster than the cold air mass.
• The warm air mass then flows over the cold air mass.
• As the warm air rises, it cools.
• This brings about clouds and sometimes light precipitation.
• Warm fronts move slowly and
cover a wide area.
• After a warm front passes,
the warm air mass behind it
brings warmer temperatures.
Section 1.2
UNIT 2
Chapter 1: Inquiring about Weather
Occluded Front
• With an occluded front, a warm air mass becomes trapped
between two cold air masses.
• The warm air is lifted up above the cold air.
• Cloudy weather and precipitation along the front are typical.
Section 1.2
UNIT 2
Chapter 1: Inquiring about Weather
Section 1.2
Stationary Front
• Sometimes two air masses stop moving when they meet.
• These stalled air masses create a stationary front.
• Such a front may bring clouds and precipitation to the same area
for many days.
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.
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.