Download Heat Transfer in the Atmosphere

Heat Transfer in the
Atmosphere
Hot or Not? Why?
Energy in the Atmosphere
 Nearly all energy in the
Earth’s atmosphere comes
from the sun.
 Energy travels to the Earth in
the form of electromagnetic
waves.
 Waves are classified by
wavelength, or the distance
between waves.
 Most of the energy from the
sun reaches the Earth in the
form of visible light and
infrared radiation, and a small
amount of ultraviolet
radiation.
 Infrared radiation is a form
of energy with wavelengths
longer than red.
 Infrared is not seen, but can
be felt as heat.
What Happens to UV Radiation?
• UV rays have wavelengths shorter than violet,
so they have more energy.
• UV rays can cause skin and eye damage.
• Energy from the sun is absorbed by within the
atmosphere by water vapor, CO2, clouds, dust,
and the ozone layer.
• Clouds reflect radiation back into space
• Dust and other gases scatter radiation in all
directions
• The Earth’s surface absorbs radiation, and
reradiates it as longer wave infrared (heat)
Greenhouse Effect
Molecules of greenhouse gases (water vapor
and carbon dioxide)
Absorb infrared radiation radiated from the
earth’s surface
Causes molecules to vibrate- transforming
absorbed energy into heat in the troposphere
This process keeps the troposphere at a
reasonable temperature for life.
Heat vs. Temperature
 Matter is made up of atoms or
molecules that are vibrating and
has energy of motion (kinetic
energy)
 When a substance is heated,
the molecules move faster and
the temperature rises.
 Heat is a form of energy
 Heat is the total kinetic energy
in an object.
 Temperature is related to
intensity, such as the degree of
“hotness”.
 Temperature is a measure of
the average kinetic energy.
(so, thermometers measure the
average energy in an object.)
 Heat moves from the higher
temperature substance to the
lower temperature substance.
Three Methods of Heat Transfer
 Conduction- transfer of heat through
matter by molecular activity
 Convection – is the transfer of heat by
movement of heated material (usually in
liquids and gases)
 Radiation – transfer through wave energy
Conduction
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Conduction is heat
transfer from molecule to
molecule
If someone touches an
ice cube or hot plate they
know because the heat is
transferred from the
warmer object to the
cooler object from
molecule to molecule.
Remember heat always
travels from high
concentration to low
concentration. If
something feels cold, it is
because the heat is going
from you to it.
Conduction - continued
Conduction QuestionsSuppose a human
could live for two
hours (120 minutes)
unclothed in air at 10
C.
How long could he
live in water at 10 C?
How do the thermal
conductivities of water
and air compare?
Convection
 Convection is heat transfer
by a circulation of rising warm
material (less dense) and
sinking cooler material
(denser).
 Convection is the most
effective method of heat
transfer for liquids and gases.
 Heated molecules expand,
become less dense and rise.
 Meanwhile, the cooler, more
dense material above drops
to replace the rising
molecules
 This is known as a
convection current.
No Convection- No Clouds
Natural Convection
Convection in the Earth
Convection- continued- How does
convection work in your home? In
a freezer?
Conceptual questions 
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Explain the following:
Wind chill factor.
Drapes hung close to a cold window.
Clothing- To keep warm on a cold day,
should you wear a fur coat with the hair
inside, or out?
Should you lower the blinds and draw
the curtains on a hot day?
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Radiation
Radiation is heat
transferred by infrared
waves.
We have all felt the
warmth of the sun or heat
from a camp fire without
touching them.
We also know that light
colored clothing reflects
the heat and dark absorbs
the heat.
This is all due to infrared
radiation or radiant heat.
We also know that on a
summer day, the infrared
gets in our car and heats
it up, but is absorbed
inside the car and when
you open the door.
Radiation - continued
 Summer clothing: white
reflects radiant energy
better than black.
 Until equilibrium is
reached, white stripes on
roads are at a lower
temperature than
unpainted asphalt.
 Wrap an ice-cube in
black cloth and another
in aluminum foil and place
both in the
sunshine. What will
happen?
Radiation – solar panels
Challenge Questions
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The sun goes down, snow falls on cement playground
and on an asphalt road.
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Why does the snow on the road melt sooner than on the
cement?
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Two different materials at the same temperature have
different emissivities. Which one glows the brightest?
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Why are fireplace pokers made of iron and not copper?
Some animals have hair which is composed of solid
tubular strands, while others have hollow, air-filled
tubes. Where would one more likely find the latter
animal: In cold climates, or warm?
Conceptual Questions
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When one steps from a shower on a cold
morning, why does the tile floor seem so much
colder than the air?
Place a wooden spoon and a metal spoon in the
freezer.
Which will cool faster? After several hours,
what would they feel like?
Why do people become "flushed" when
overheated?