Transcript 11.0 Energy in the Atmosphere

10.2 Energy Transfer in the Atmosphere
• Earth’s atmosphere is a key factor in allowing life to survive here.
 This narrow band of air has the right ingredients, and maintains the correct
temperature, to allow life to form and survive.
.
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10.2 Energy Transfer in the Atmosphere
 Originally, Earth’s
atmosphere was very
different, and had no oxygen.
 Scientists think that early
volcanic activity from large
volcanoes released large
amounts of water, CO2,
methane (CH4), sulphurcontaining gases and
hydrogen into the
atmosphere.
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10.2 Energy Transfer in the Atmosphere
• Scientists think that oxygen first came from the breakdown of water
by sunlight, then later by photosynthesis by photosynthetic bacteria
(cyanobacteria) and plants.
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10.2 Energy Transfer in the Atmosphere
 Air on Earth today is 78% N2, 21% O2, 0.92% Ar, 0.04% CO2 and a variety of
others.
 The density of the atmosphere decreases with altitude.
The composition of
Earth’s atmosphere.
See pages 436 - 437
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The 5 Layers of the Atmosphere
 The troposphere: Closest to
Earth’s surface, 8 km - 16 km thick
 Highest density layer because
all other layers compressing it
down.
 Almost all water vapour in the
atmosphere is found here.
• Therefore, this is where
most weather takes place.
• Solar energy and thermal
energy from Earth keep air
moving
 Temperatures range from
average of +15ºC at the bottom
to –55ºC at the top.
See pages 438 - 439
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The 5 Layers of the Atmosphere
 The stratosphere: The second layer,
above the troposphere
 10 km to 50 km above Earth,
warming from –55ºC as altitude
increases
 The transition from troposphere to
stratosphere is called the
tropopause.
 The air is cold, dry and clean in the
stratosphere.
 Has strong, steady winds, and
planes often fly here to avoid the
turbulent troposphere.
 The ozone layer is found here, which
blocks harmful UV radiation.
• This is why the upper
stratosphere warms more
See pages 438 - 439
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The 3 Layers of the “Upper Atmosphere”
 The mesosphere: 50 km to 80 km above Earth
 Temperatures are as low as –100ºC
 This layer is where space debris burns up when it
begins to hit particles
See pages 438 - 439
The layers of Earth’s atmosphere.
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The 3 Layers of the “Upper Atmosphere”
 The thermosphere: 80
km to 500 km above
Earth
 Temperatures can
reach +1500ºC to
+3000ºC
 This is where the
Northern Lights,
aurora borealis, are
found.
• Charged
particles in
Earth’s magnetic
field collide with
particles in the
thermosphere
which heat it up.
See pages 438 - 439
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The Aurora Borealis (Northern Lights)
• When charged particles captured by the magnetosphere collide with
the thermosphere particles in the vicinity of the earth’s poles, they
release energy seen as moving lights of various colors, the Aurora
Borealis.
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The “Upper Atmosphere”
• The exosphere: 500 km to 700 km, where it
merges with outer space.
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Radiation and Conduction in the Atmosphere
• Almost all of the thermal energy on Earth comes from the Sun
 But only about 50% of the solar radiation reaches the Earth’s surface.
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Radiation and Conduction in the Atmosphere
• Incoming solar radiation is reflected and absorbed by clouds and
atmospheric particles.
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Radiation and Conduction in the
Atmosphere
 Most thermal energy is
transferred near the equator,
which receives a much more
direct source of solar
radiation.
 Insolation = amount of solar
radiation an area
receives, measured in W/m2)
 Insolation decreases if
there are particles of
matter (dust, smoke) in the
way, or if the angle
of incidence of the solar
radiation is too great.
Angle of incidence
See pages 440 - 441
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Radiation and Conduction in the Atmosphere
 Solar radiation does not heat the atmosphere directly.
 Earth’s surface absorbs solar radiation, heats up, then
re-radiates the thermal energy into the atmosphere.
• This provides 70% of the air’s thermal energy!
 Convection in the air spreads the thermal energy around.
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The Radiation Budget: Where Solar Radiation
Goes
 If all 342 W/m2 of solar radiation that reaches Earth was stored in the
atmosphere, it would be far too hot to support life as we know it.
 Earth’s radiation budget = heat gained – heat lost
See pages 442 - 443
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The Radiation Budget: Where Solar Radiation
Goes
 Of the of the solar radiation
that comes into earth’s
atmosphere, 15% is reflected
by clouds back into space, 7%
is reflected by particles back
into space, 20% is absorbed
by clouds and 58% reaches
Earth’s surface
• 9% of this amount is
reflected back out into
space by Earth’s
surface
• 23% drives the water
cycle, 7% creates wind,
and 19% is re-radiated
from Earth’s surface.
See pages 442 - 443
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The Radiation Budget: Where Solar Radiation
Goes
 When Solar radiation
reachs the Earth’s
surface (58%),
• 9% of this
amount is
reflected back
out into space
by Earth’s
surface
• 23% drives the
water cycle, 7%
creates wind,
and 19% is reradiated from
Earth’s surface.
See pages 442 - 443
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Albedo
• Albedo refers to the amount of energy reflected by a surface.
 Light-coloured surfaces have a high albedo, and reflect energy (snow, sand)
 Dark-coloured surfaces have a low albedo,
See pages 442 - 443
and absorb energy (soil, water)
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What Is Weather?
•
Weather is the conditions in the atmosphere at a
particular place and time.
 “Weather” describes all aspects of the atmosphere, and is closely related to
the transfer of thermal energy.
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Atmospheric Pressure: The Cause
 We exist at the bottom of a sea
of air which is above us.
 Since we have kms of air above
us, the air above us exerts
pressure on us.
 This is like when we go down in
water, we experience an
increase in pressure due to the
water above us.
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Atmospheric Pressure discover by Torricelli
 Evangelista Torricelli made the first barometer to
measure atmospheric pressure.
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What holds up the mercury in a barometer?
 The pressure of the
kms tall air column
over the mercury
dish equals the
pressure that the
mercury column
exerts.
 At sea level on a fair
day, the height of
the mercury column
will be 760 mm.
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Atmospheric Pressure changes with altitude
 Blaise Pascal, a young French scientist built a barometer and brought it along on a
hike up a mountain.
 He made a hypothesis that the column of mercury should drop as he went up the
mountain since the air column above him would be less as he rose up the mountain.
 Measuring the barometer column height, Pascal found that it dropped as he hiked up,
verifying that his hypothesis was correct.
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Atmospheric Pressure
 Torricelli observed that the barometer column rose the highest during sunny
weather but that it dropped to lower levels during cloudy and rainy weather.
 This meant that drier air was heavier than damp air.
 Aneroid barometers use springs and pressure canisters to record air pressure
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How can dry air be heavier than wet air?
 Equal volumes of any gas
(including air) at the same
temperature and pressure have
equal numbers of molecules
(Avogadro’s Principle).
 Water molecules (H2O = 18u) are
lighter than either nitrogen (N2 =
28u) or oxygen (O2 = 32u).
 When water molecules in damp
air replace oxygen and nitrogen
molecules, the air sample thus
gets lighter.
See pages 443 - 446
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Normal Atmospheric Pressure: Sea Level, Sunny
Day, Normal humidity
 Atmospheric pressure, measured with a barometer, is the amount of pressure
the molecules in the atmosphere exert at a particular location and time.
 Atmospheric pressure is measured in kilopascals (kPa) = 1000 N/m2
 At sea level, atmospheric pressure = about 1 kg/cm2, 760 mm, 14.7 pd/in2,
1008mb (millibars), 1 atm (atmosphere), 101.3 kPa, 101300 Pa, 29.92 in,
1013 hPa
See pages 443 - 446
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Air Pressure Change Summary
 Warmer air expands and is less
dense, so it produces less air
pressure than colder air.
 Wetter air is lighter so it produces
less pressure than drier air.
 Air pressure at higher altitudes is
less because there is less air
above the earth at these places.
 Colder air can hold less water
(humidity) than warmer air so cold
air exerts more air pressure
because it is more dense and has
less water.
 Warm, moist air exerts less air
pressure because it is less dense
and has overall lighter molecules.
See pages 443 - 446
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Air Pressure Effects on Planes
• Low Pressure air
masses cause planes
to drop.
• When taking off,
planes need less
takeoff distance if the
pressure is higher.
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Humidity
 Humid air (air with more water vapour) has
lower pressure than dry air.
• With pressure drops, meteorologists know
warm, moist air is arriving in the area.
• Specific humidity = the total amount of
water vapour in the air
 Dew point = the temperature where no
more water vapour can be held by air,
so water droplets begin to form.
• Relative humidity = the percentage of water
that the air that is currently holding
compared to what it could hold.
 45% relative humidity means that the air
is holding 45% of the water vapour it
could before reaching its dew point.
 As air warms, it can hold more water.
 If cool air is warmed without adding
water, its relative humidity drops.
See pages 443 - 446
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Convection in the Atmosphere: Wind Cause
Wind is the
movement of
air from high
pressure to low
pressure.
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Air Masses: Where They are Produced
 An air mass is a large
body of air with similar
temperature and
humidity.
 Air masses take on the
conditions of the
surface (land/water)
below.
 Air masses can be as
large as an entire
province, or even
larger.
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Air Masses: Their Characteristics
 Arctic air masses are
cold and dry since
cold air holds much
less moisture.
 Maritime air masses
are moist and either
cool or warm
depending on their
latitude.
 Continental air
masses tend to be
drier and can be cool
or warm depending on
latitude.
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Weather Systems: High Pressure Systems
• High pressure systems form when an air mass cools.
 This usually occurs over cold water or land.
 Winds blow clockwise around the center of the high.
See pages 447 - 448
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Prevailing Winds
• Prevailing winds are winds that are typical for a location.
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For example, winds in BC usually blow in from the ocean.
Precipitation falls as air is forced up the mountain slopes.
Air gets drier as it moves inland, continuing to drop precipitation.
Dry air rushes down the far side of the mountains into the prairies.
The prevailing winds off BC’s coast, crossing into Alberta.
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The Coriolis effect
Winds move from high
pressure to low pressure.
 In a simple model, air
would warm in the tropics,
and rise.
 Cooler air from the north
would rush in below to fill
the empty spot.
 The warm air at higher
altitudes would move
north to replace the cooler
air.
 This occurs at several
latitudes as we move
north.
Wind systems of
the world.
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The Coriolis effect
As earth rotates, these
winds are ‘bent” clockwise
in northern hemisphere
and counterclockwise in
the southern hemisphere =
Coriolis effect
 The equator moves much
more quickly than the poles.
Wind systems develop
 The trade winds
 The prevailing westerlies
 The polar easterlies
Wind systems of
the world.
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Wind Zones on Earth
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Jet Streams
Strong winds occur in areas
between high and low
pressure systems.
 The boundaries between the
global wind systems thus have
very strong winds.
 In the upper troposphere,
between warm and cool air, are
the jet streams.
 Jet streams often look like
streams of water.
 The Polar jet stream can
move at 185 km/h for
thousands of miles.
 Planes flying east across
Canada “ride” the jet
stream, and avoid it flying
west.
See page 451
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Jet Streams Vary Seasonally
• The jet stream moves north during the summer season and south
during the winter season.
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Jet Streams Vary Daily
• The jet stream moves daily due to changes in pressures and weather
fronts.
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Local Winds
Local winds arise and are influenced by local geography.
 In BC, sea breezes blow inland (onshore breeze) when the land warms in the morning,
and outward (offshore breeze) when the land cools in the evening.
See page 451
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Fronts: Cold Front
A front is a
boundary
between two
different air
masses.
 Cold air forces
warm air to
rise, so fronts
usually bring
precipitation.
 Rain falls
behind the
leading edge
of a cold front
See page 451
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Front: Warm Front
• Rain falls along the forward side of a warm front.
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Fronts: Occluded Front
• When cold air fronts meet and lift a warm air mass, this is called an
occluded front.
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Fronts: Occluded Front
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Fronts: Stationary Front
• Rain falls on the cold air mass side of a stationary front.
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Weather Involves Interaction of Fronts
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Extreme Weather
Air masses often have
very large amounts of
thermal energy.
 Extreme weather can arise
under certain conditions as
this energy is released.
 Thunderstorms occur when
warm air rises, water
condenses (which releases
even more energy), building
the thunderhead even
higher.
 Static energy can be
built up and released as
lightning.
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Extreme Weather
Air masses often have
very large amounts of
thermal energy.
 Sea breezes in the
tropics, and energetic
cold (and even warm)
fronts can cause
thunderstorms.
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Extreme Weather: Tornados
• Tornadoes form when thunderstorms meet fast horizontal winds (Jet S).
 A “funnel” of rotating air may form, which sometimes extends all the way to the
ground with winds of up to 400 km/h.
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Extreme Weather: Hurricanes and Typhoons
The tropics, with their intense heat, can often have
severe weather.
 Large masses of warm, moist air rise quickly, and cool air
rushes in.
 Counter-clockwise in the northern hemisphere, clockwise
in the south (See upper right of Australian typhoon).
Hurricanes = Tropical cyclones = Typhoons
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Extreme Weather: Hurricane
• As warm moisture condenses, it releases more energy that fuels the
winds and expands the hurricane. The longer a hurricane develops
over warm water, the more destructive it gets.
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Extreme Weather: Hurricane Locations
• Warm waters at latitudes of 20 degrees from the equator often get
warm enough to generate hurricanes.
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