Chapter 13 & 14.
1
Weather dynamics is the study of how the
motion of water and air causes weather
patterns.
Energy from the Sun drives the motion of
clouds, air, and water.
A globe is tilted to represent Earth’s tilt at an
angle of 23.5 degrees to the plane of its orbit
around the Sun.
The major components of Earth that influence
weather are the atmosphere, the land forms,
and water in its solid, liquid and vapour
forms.
About 70% of Earth’s surface is covered by
oceans.
2
The atmosphere above the oceans and
continents contains air, water vapour, and
particles of dust and chemicals, all of
which affect weather, especially when the
atmosphere is in motion.
3
Weather is the set of environmental
conditions encountered from day to
day.
Climate is the set of environmental
conditions averaged over many years.
A city may have a January climate that
is cold, but you could have a week of
mild weather.
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4
Longitude is the angle measured east or west from
the 0 degree line which passes through Greenwich,
England.
The eastern tip of Cape Breton Island is at
60 degrees west longitude.
Latitude is the angle measured north or south
of the equator. The border between the US and
our western Canadian provinces is along the
49 degree north latitude line.
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5
The Tropic of Cancer is at 23.5 degrees north
latitude. It is the most northerly location reached by
the Sun’s vertical rays on the first day of summer,
June 21, each year.
The Arctic Circle is at 66.5 degrees north latitude. It
is the most northerly location reached by any of the
Sun’s rays on the first day of winter, December 21.
In the southern hemisphere we have the Tropic of
Capricorn and the Antarctic Circle.
The region between the Tropic of Cancer and the
Tropic of Capricorn is referred to as the tropics.
Polar regions occur north of the Arctic Circle, and
south of the Antarctic Circle.
Most of Canada’s population lives in the mid-latitude
region.
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6
Section 13.2
7
Almost all of the energy used on Earth to sustain life
and cause our changing weather systems comes from
the Sun. Different types of EM energy are emitted
from the Sun.
Without this energy plants would not grow, and the
land water and air would not be warm enough for
people to survive. The average surface temperature is
15 degrees C.
Energy can be transferred from one place to another
by 4 methods:
1)
2)
3)
4)
Radiation
Conduction
Convection
Advection
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8
Radiation is the transfer of energy by means of waves.
Unlike water and sound waves, radiation does not
need a medium. The waves can travel from the Sun,
through space, and reach Earth.
Visible light is an example of energy that can travel
through space. Other examples are:
1) Radio waves
2) Microwaves
3) X-rays
4) Gamma rays
5) Infrared rays
These travel at 300,000 km/s in a vacuum.
9
The set of waves that can travel through empty
space at the speed of light is called the
electromagnetic spectrum.
10
The other methods of energy transfer require
particles of matter.
Conduction is the transfer of energy through the
collision of particles. Conduction occurs most
easily in metals , but also to a smaller extent in
rock, sand soil and water.
11
Convection and advection are the transfer of
energy by the movement of particles in a fluid. A
fluid is either a liquid (water) or a
gas(atmosphere).
Convection transfers energy vertically .
Advection transfers energy horizontally.
Weather systems involve convection and
advection.
12
When the EM waves from the Sun reach Earth, some is
reflected off the atmosphere and clouds back into
space; some pass through the atmosphere and bounce
off Earth’s surface; some get absorbed by the
atmosphere, the ground, or the water at the surface.
13
For earth materials, the portion of energy
reflected depends on the albedo of the material.
Clean snow has a high albedo, it reflects a lot of
incoming energy. Black soil has a low albedo, it
absorbs more energy than it reflects.
Any object or material that absorbs energy and
becomes warmer is called a heat sink.
Even though water has a higher albedo than land
and soil, the oceans are good heat sinks. When
solar energy hits water , the water begins to
move(convection), and transfer energy deep into
the oceans.
Soil and rock are poor heat sinks. Heat is
conducted slowly into these materials.
14
An important property of all substances is their
heat capacity, which is the measure of how
much heat a substance requires to increase its
temperature or how much heat it releases as its
temperature decreases.
Water has a high heat capacity. This means it
can hold a lot of heat.
15
Section 13.4



The thin layer of gases that surround the
earth is the atmosphere.
The atmosphere is where all the weather
happens.
The atmosphere acts like a blanket which
controls the temperature of the earth.
17
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


The earth's atmosphere is made up of dust
and a mixture of invisible gases. Some of
these gases include:
Nitrogen (N2) 78%
Oxygen (O2) 21%
Other gases: 1% combined
[water vapour, argon, carbon dioxide, neon,
helium, krypton, hydrogen, ozone...]
18



Nitrogen and ozone act as a protection
shield that blocks out harmful radiation
from space.
Oxygen is essential for life. Plants
produce oxygen and we breathe it in.
Carbon dioxide is essential for life
too. We breathe out carbon dioxide and
plants breathe it in.
19



Water vapour is essential to the water cycle
and weather patterns.
Water vapour is responsible for clouds, fog,
rain and snow.
Note: Even though there is not much water
vapour in the atmosphere it has the greatest
effect on the weather.
20
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The atmosphere can be divided up into
distinctive layers. The farther we travel from
the earth the thinner the atmosphere gets.
Exosphere
Thermosphere
Mesosphere
Stratosphere
Tropopause
Troposphere
21
Troposphere
•
•
•
•
The atmospheric layer closest to Earth’s surface
Up to 16 km at equator, 8 km at the poles
Contains most of the atmosphere’s moisture
Responsible for most of our weather
Tropopause
• Troposphere ends in this thin boundary
• Temperature no longer decreases with increasing altitude
• Temperature rises here, contains ozone which absorbs UV
from the Sun
• Higher temperature here helps divide troposphere from
stratosphere
22
Stratosphere
• Dry layer
• From 12 to 50 km
• Highest ozone levels O3
• Protects Earth from harmful UV
• Temperature increases with
altitude
Mesosphere
• Temperatures are low (-75oC)
• Density of gases is low
• 50 km to 80 km
23
Thermosphere
• Low density
• Molecules have higher energy
• Higher temperatures than
mesosphere
• Temperatures up to 30oC
• X-rays absorbed, causing high
temps
• 80 km to 500 km
• Sometimes called ionosphere
• Particles charged and produce
auroras
24
Exosphere
• Outermost layer
• Can be called space
• Few particles, mainly
hydrogen
Note that the temperature of the atmosphere is
different at different altitudes. Change in
temperature over a distance is called a temperature
gradient.
The temperature gradient of the troposphere is -6 oC
per 1000 meters.
25
Atmospheric pressure is the pressure the air exerts as
gravity pulls it toward the center of Earth.
It is greatest at sea level, where the molecules are closet
together.
At higher altitudes atmospheric pressure decreases.
Atmospheric pressure at a particular altitude depends on
whether the air is rising or falling. There are two variations
to consider :
vertical and horizontal.
Pressure gradient is a measure of the amount the
atmospheric pressure changes across a set distance.
Pressure gradients can be vertical or horizontal.
26
Atmospheric pressure decreases rapidly as the
altitude increases. Mountain climbers and air
travellers know about atmospheric pressure.
Weather maps show lines of constant pressure.
The gradient is greatest where the lines are
closest together. High and low pressure systems
are identified on these maps.
27
The most common instrument used to measure
atmospheric pressure is the aneroid barometer.
The word aneroid means without liquid.
This instrument consists of an enclosed container
with thin metal walls that are sensitive to pressure
changes. A needle attached to the container
indicates the pressure.
(air pressure drops and the container expands)
An aneroid barometer uses a small, flexible metal
box called an aneroid cell. This aneroid capsule
(cell) is made from an alloy of beryllium and
copper.
28
A barometer is commonly used for
weather prediction, as high air pressure
in a region indicates fair weather while
low pressure indicates that storms are
more likely.
If the barometer is falling then
deteriorating weather or some form of
precipitation will fall, however if the
barometer is rising then there will be
nice weather or no precipitation.
29
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Gravity pulls down on all matter.
Gases are matter and gravity pulls down
on them.
This is why the troposphere (layer
closest to the earth) has 99% of all the
gases in the atmosphere.
30
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

The atmosphere is made up of areas of
different densities.
In some areas the air is compacted very
tightly (dense) and is very heavy causing
a high pressure area.
Other areas the air is not compacted
much at all and the air is very light (less
dense) creating a low pressure area.
31

The air at high altitudes is much thinner
(less dense) creating low pressure and
cooler temperatures.
32
Section 13.6
33



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Sailors discovered that in certain areas the winds
tend to blow in the same directions most of the
time.
They found that if they sailed south close to the
equator the winds would blow to the west (from
the east).
As they traveled further north they found that the
winds would blow most often to the east (from
the west).
This regular pattern of winds is known as
prevailing winds.
34

A wind is a movement of air in the
atmosphere. Major wind patterns cover
large areas and are called prevailing winds.
These winds affect weather around the
world.
35

Winds that affect large areas in regular
patterns.

Blowing to the east they called the
Northeast trade winds.

The winds blowing from the west (taking
them back home) were called the
mid-latitude Westerlies (prevailing
Westerlies).
36
37
Heat
 As the sun heats the air over the equator
strong convection currents form.


The hot air rises up and air rushes in
from the north and south creating winds
toward the equator.
This huge convection current billows out
and the air begins to cool and fall down
around 30o latitude.
38




As the air falls some of it returns to the
equator but some is deflected northward.
This north flowing air is once again heated
and rises up at about 60o latitude.
This rising air then flows to the north pole
where it cools and drops flowing back to
the 60o latitude.
We now have three convection currents setup with air flowing in opposite directions at
the surface of the earth.
39
Spin
 The earth rotates east to west.

As the earth spins it deflects the wind.
◦ Winds blowing north get deflected to the right.
◦ Winds blowing south get deflected to the left.

The deflection of the wind caused by the
earth's rotation is called the Coriolis effect.
40
Earth’s rotation causes anything that moves long
distances, such as prevailing winds, to appear to
change direction. This apparent change of direction of
a moving object in a rotating system is called the
Coriolis effect.
Viewed above the North pole, Earth rotates eastward or
counter clockwise. Objects in the Northern hemisphere
appear to move to the right. In the Southern
hemisphere moving objects appear to move to the left.
From some point in the northern hemisphere, fire a
rocket at a target south of your position. Because the
Earth is rotating the target moves and the rocket will
miss its target.
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42
43
44
Early explorers like Columbus used trade winds
to cross the Atlantic Ocean.
45
Prevailing winds are caused by a combination of convection
currents and Earth’s eastward rotation.
In the Northern hemisphere....
• Solar energy strikes the equator, heating the air, land,
water
• This warmed air becomes the equatorial convection
current
• The warm air rises and expands, leaving a low pressure
area
• Rising air reaches the troposphere, moving northward
• At 30 degrees latitude the cooled air sinks, creating high
pressure
• Air moves from high to low pressure areas at the equator
• The moving air is twisted right as it moves south
(Northeast Trade Winds)
46
In the Northern hemisphere.....
At 30 degrees latitude some descending air from
the equatorial convection current is deflected
northward, to an area of low pressure at 60
degrees latitude. This low pressure area is formed
by the mid-latitude convection current. The surface
air moving northward to the low pressure area
twists to the right causing the mid-latitude
westerlies.
47
At the North Pole the air is cold and dense, so
it sinks, creating a high pressure region at the
surface. This surface air moves south, twisting
to the right and creating the polar easterlies.
48
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A narrow band of spinning air is created in
the places where these convection currents
rise and fall.
The spinning causes the air to speed up
creating a tube of fast moving air known as
a jet stream.
The winds of the jet stream travel from west
to east and can reach speeds of up to
roughly 500 km/h.
49

Aircraft use this to their advantage when
flying form west to east.
◦ pick up to a 500 km/h tail wind which saves
time and fuel.


Going from east to west pilots try to avoid the
jet streams.
Jet streams go right around the
globe and generally steer major
weather systems.
50
51
Jet Streams – high speed winds in the troposphere
Air moves from higher to
lower pressure areas.
The troposphere is thicker
at the equator, decreasing
northward. So pressures
will vary.
We get a high altitude
east-ward flowing wind at
30 degrees latitude, and
again at 60 degrees
latitude. Both air masses
twist to the right.
(241 to 482 kilometres per hour)
52
53
Prevailing winds and the jet streams are affected by
seasonal changes.
Prevailing winds help to distribute large amounts of solar
energy from the equator to colder parts of the world.
Convection currents create a return flow of air southward.
Prevailing winds carry moisture causing rain, snow.
Rising air is warm and moist.
Falling air is cool and dry.
At 30 degrees N latitude we have cool, dry air. Many deserts
are found in this latitude.
At 60 degrees N latitude two air systems meet and rise
giving birth to winter storms.
54
Section 13.8
All of Earth’s water, both fresh and salt, forms what is called
the hydrosphere. About 70% of Earth’s surface is covered by
water.
Freshwater makes up 2.5% of the total water on Earth. Most
of this occurs as polar ice.
Energy from the Sun causes water to evaporate(liquid to vapour)
or ice to sublimate(solid to vapour). The invisible water vapour
rises , and when the pressure and temperature decrease, the
vapour condenses(vapour to liquid) into fog, mist and clouds.
Sometimes water vapour may do the reverse of
sublimation(deposition) and form ice crystals. The precipitation
falls and the cycle begins again.
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Section 13.9
58

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
In 1992 a container ship in the middle of the Pacific
Ocean lost 29 000 bath tub toys over the
side. Rubber duckies started washing ashore all over
the west coast of North America.
In 1990 in a similar type accident 80,000 pairs of
Nike shoes were swept off a Korean ship headed for
the United states. Nike shoes started showing up
from Hawaii to Oregon and as far north as Alaska.
These two accidents provided valuable information to
oceanographers regarding ocean currents.
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60
Another spill
occurred in
1999.
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An oceanographer is a scientist that
studies ocean currents.
Ocean currents are compared to large
conveyor belts that move around the
globe.
The ocean currents circulate the sun’s
energy from the equator to the poles.
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They serve to warm the poles and at the same
time cool the waters of the equator.
In other words the ocean current spread out
the heat energy all over the earth so that one
area doesn't become too hot or too cold.
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The main cause of ocean currents is
heating of the ocean by the sun.
At the equator the sun strongly heats the
water.
As the water warms is gets lighter (less
dense) and begins to rise.
Cooler, denser water sinks and rushes in
to replace the warmer water.
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
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This movement of water creates
enormous convection currents.
We see warm surface currents flowing
toward the poles (N & S).
At the same time, we get cold deep water
currents flowing toward the equator.
The surface currents are pushed along
and steered around the earth by the
prevailing winds.
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67

The warmer the air is above a body of
water, the more water it is capable of
holding.
◦ Evaporation rate is high and clouds form.
◦ Large amounts of precipitation.

Colder water has cool and dry air above it.
◦ Weather it brings is cool and dry.
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The Gulf Stream warms the coast of Norway and Iceland.
Ocean currents are like air- the warmer a body of air the
greater its ability to hold moisture. The current that
reaches Peru is cold so the air above it is cold and dry. We
get the Atacama desert on the coast. Where warm waters
evaporate, clouds and precipitation form.
Ocean currents keep coastal areas cooler in summer and
warmer in winter. We are warmed in winter by warm, moist
air of the Gulf Stream.
Ocean currents affect the pressure of the air above them.
Air above warm ocean currents rises and forms low
pressure systems.
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Average winter temperature for Ottawa is 12°
colder than in St. John’s even though Ottawa
is further South!
The warm, moist
air brought northward by the Gulf
Stream off the
coast of NL is the
reason.
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El Niño
 The phrase El Niño has been around for a
long time.


El Niño was originally just considered a
gentle warming of the Pacific Ocean near
the west coast of South America.
It usually occurred around Christmas time
each year in which local people related the
El Niño with poor fishing.
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Normally the wind blows off the land in
South America pushing away the warm
surface water.
The cold nutrient rich water rises up
(upwelling) and fish thrive.
During the El Niño wind patterns change
and warm surface water is no longer
pushed away.
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Since the water is not circulating it
cannot cool.
The cold water with all its nutrients is
trapped and cannot rise up.
No nutrients getting to the surface
means poor fishing and fish kills!
74
Normal Year
El Niño Year
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During an El Niño year the Pacific Ocean
undergoes a greater than normal amount
of heating.
The extra heating disrupts and changes
the normal patterns of convection
currents and wind patterns in the Pacific
Ocean.
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A long lasting El Niño effect is believed
to affect the weather of the entire
planet.
Major shifts in winds and current
patterns create weather extremes that
bring major ecological, social and
economic disruptions world-wide.
The direct cause of El Niño is unknown
but it is believed to be connected to
global warming.
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During El Niño years the jet stream tends
to push further north.
Air north of the jet stream is cooler than
air south of the jet stream.
As result North America tends to receive
warmer than normal average
temperatures.
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
During an El Niño year in Newfoundland
we would get a warmer winter than
normal which would mean more rain and
less snow!
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About every four to five years, a pool of
cooler-than-normal water develops off
South America.
The effects of this cooler water are called
La Niña.
This usually shifts the jet stream farther
south which steers’ colder drier winters
to the Canadian west.
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
For Newfoundland it may bring cooler
wetter conditions - lots of snow!
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1.
2.
3.
4.
5.
6.
7.
8.
The Sun’s Energy
Cloud Cover
Earth’s Rotation
Jet Streams
Prevailing Winds
Ocean Currents
Land Masses
The Hydrosphere
p. 536 A Global Weather Model
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Section 13.11

As air rises it begins to cool and expand.

Cooled air can no longer hold all its moisture.


The water vapour begins to condense on dust
particles as very tiny water droplets.
Depending on the temperature clouds may be
made up of tiny water droplets and or tiny ice
crystals.
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1. Convective: formed when a land mass is
heated and the warmed air begins to rise,
expand, cool and water condenses.
We see these types of clouds where thermals
and sea breezes are formed.
•
•
•
•
•
When air near the ground is heated
Warm air rises, carrying moisture
At higher elevations air cools
Water vapour condenses, forms clouds
Occurs where solar energy absorbed by water and
other surfaces
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2. Frontal:
form at the frontal zone where two large
air masses meet.
The warmer air mass is forced to rise up
over the cooler air mass.
It expands and cools resulting in the
formation of condensation.
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3. Orographic:
formed because of geography when air is
forced to rise up a large hill or
mountain.
As the wind blows into the side of the
mountain it rises up.
As the air rises it expands and cools
causing water vapour to condense as
clouds.
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•
•
•
•
•

A cloud that forms near the ground
Can form on cool, cloudless nights
When warm air passes over snow-covered ground
When moist sea air drifts over a cold current
When moist air rises up a mountain side
Forms when warm moist air moves over a colder surface
(land or water) releasing its moisture as very fine water
droplets.
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Cloud shapes tell us about atmospheric
conditions.
Two general shapes of clouds:
1. Cumulus Clouds
2. Stratus Clouds
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

Heaped" or "lumpy" clouds result when strong
vertical (upward) motions exist in the
atmosphere.
This shows us that the air mass is being
forced to rise very rapidly.
A clue that the atmosphere is unstable and
are usually associated with stormy or severe
weather.
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

Wide spread out, smooth, layered
clouds.
These clouds gives a clue that the air
motion is horizontal (across) rather than
vertical (up and down).
The forming clouds are rising slowly
which is a sign of a stable atmosphere.
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99
To further classify clouds, they are named by
altitude in the atmosphere.
Low level clouds have simple names –
cumulus and stratus
Medium level clouds – start with prefix alto –
meaning higher
Higher level clouds – called cirrus which
means curly hair
10
0
altocumulus
stratocumulus
10
1
cumulonimbus
10
2
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Evening-May
3,2009
104

Clouds have a duel role:
1) Quite simply clouds act as a blanket.
◦
◦
Cloudy nights: traps heat keeping the air warm.
Clear night sky: heat escapes and air cools quickly.
2) Keep the earth cool during the day.
◦ The formation of white cloud cover reflects the
sun's energy away.
105
When is there a greater risk of frost, on a
cloudy night or a clear night?
Deserts regions are so dry that clouds do
not form during the day or the night.
What do you think the temperature
conditions would be like?
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