EARTH’S ENERGY BALANCE
EARTH’S ENERGY BALANCE
(Heat and Temperature)
(Heat and Temperature)
What happens to solar
radiation as it travels
through the atmosphere?
ENERGY ESSENTIALS
ENERGY ESSENTIALS
• InIncoming coming solsolar radiar radiationation ( (insolationinsolation) is the primary energy source ) is the primary energy source for the atmosphere
for the atmosphere
• Land, oceans, clouds, atmospheric gases and dust intercept Land, oceans, clouds, atmospheric gases and dust intercept insolation
insolation
• Most atmospheric gases are Most atmospheric gases are transparent transparent to solar radiation and, to solar radiation and, instead,
instead, absorbabsorb terrestrial radiationterrestrial radiation
• Energy Pathways and Principles Energy Pathways and Principles
– Input from the SunInput from the Sun: : shortwaveshortwave energy energy from the Sunfrom the Sun
– Output from EarthOutput from Earth: : longwavelongwave energy energy from Earth’s surfacefrom Earth’s surface
• Atmosphere and Earth’s surface heated by solar energy which is Atmosphere and Earth’s surface heated by solar energy which is unevenly distributed
unevenly distributed by by latitudelatitude and and seasonseason
The balance between incoming solar radiation, the
absorption of terrestrial radiation, and outgoing terrestrial radiation describes the:
“
“Global Energy Budget”Global Energy Budget”
5 5
Definitions
Definitions
•
INSOLATION:
INSOLATION:
the amount of solar
the amount of solar
radiation (energy from the Sun) that
radiation (energy from the Sun) that
reaches the Earth.
reaches the Earth.
•
ANGLE OF INSOLATION:
ANGLE OF INSOLATION:
the angle at
the angle at
which the Sun’s rays strike the Earth’s
which the Sun’s rays strike the Earth’s
surface.
surface.
•
SOLAR DECLINATION:
SOLAR DECLINATION:
The latitude at
The latitude at
which the Sun angle is 90 degrees.
Why is the angle so important?
Why is the angle so important?
Because of the
orientation of Earth’s axis of rotation to the Sun (tilted 23.5
degrees), and the fact that the orbit is an
ellipse, the angle of the Sun’s rays varies
throughout the year
The angle at which the sun’s rays strike Earth’s
The angle at which the sun’s rays strike Earth’s
surface determines the
surface determines the amount amount of solar energy of solar energy received
received per unit of surface areaper unit of surface area..
Angle of Sun’s rays = 73
Angle of Sun’s rays = 7300
Area = 1.04 m
Area = 1.04 m22 Angle of Sun’s rays = 26Angle of Sun’s rays = 26 0 0
Area = 2.24 m
Area = 2.24 m22
More than twice the area for the same amount of
More than twice the area for the same amount of
energy, so average energy is lower per unit area
energy, so average energy is lower per unit area
More energy per surface area
Sun Angle and Amount of Insolation
Sun Angle and Amount of Insolation
More direct energy per unit area
Less direct energy per unit area
Before proceeding to the next section, answer the following prompt based on information from the previous slides.
W2L: Take one minute and answer this statement:
“
“The season shown in the diagram below for the The season shown in the diagram below for the
northern hemisphere is ________________ because ………...” northern hemisphere is ________________ because ………...”
Global Energy Balance
Global Energy Balance
Atmospheric Influences on
Atmospheric Influences on
Insolation
Insolation
1.
1.AbsorptionAbsorption
2.
2.Reflection and ScatteringReflection and Scattering
3.
3.TransmissionTransmission
Radiant energy incident upon Earth’s
atmosphere is either
absorbed
,
reflected
, or
scattered
by
atmospheric gases and/or the Earth’s
surface
It is important to note that energy
reflected and/or transmitted
(scattered)
does not
contribute to
overall heating
Absorption
Absorption – transfers energy from source to absorber absorber warms
• gases, particulate matter, water
droplets absorb energy
• the amount of radiation absorbed is a function of the wavelength
(not all wavelengths are equal)
example: UV vs. visible light
• infrared radiation absorbed by CO2
and H20vapor
Reflection and Scattering
Reflection and Scattering
•
ReflectionReflection – redirection of energy without – redirection of energy without absorptionabsorption
•
All objects reflect visible light All objects reflect visible light effectiveness varies
effectiveness varies
•
Albedo Albedo – – % of visible light reflected % of visible light reflected•
There are two types of There are two types of reflectionreflection::– SpecularSpecular: light is reflected with equal : light is reflected with equal intensity (e.g. mirror)
intensity (e.g. mirror)
– DiffuseDiffuse reflection OR scattering: light is reflection OR scattering: light is reflected in multiple directions, weakly
reflected in multiple directions, weakly
(e.g. snow)(e.g. snow)
•
Radiation reaching Earth’s surface can Radiation reaching Earth’s surface can be either scattered or unscattered:be either scattered or unscattered:
– DiffuseDiffuse radiation (scattered) radiation (scattered) – Direct radiation (unscattered)Direct radiation (unscattered)
IMPORTANT: IMPORTANT:
• Scattered energy is Scattered energy is
re-directed NOT re-directed NOT absorbed
absorbed
•
Size
Size
of the of thescattering
scattering agent agent
(particle in atmosphere)
(particle in atmosphere)
relative to wavelength
relative to wavelength
determines the type of
determines the type of
scattering
scattering
3 Types of Scattering:
3 Types of Scattering:
1.
1. RayleighRayleigh 2.
2. MieMie 3.
3. Non-SelectiveNon-Selective
A discussion of each type follows…
A discussion of each type follows…
1)
Rayleigh Scattering• involves gases, smaller than the insolation wavelength
• scatters light in all directions • most effective at short
wavelengths (violet, blue)… hence, blue sky
• explains reddish-orange
sunsets when light travels through thick slice of
atmosphere
Why is the sky
blue?
2)
2) Mie ScatteringMie Scattering
– involves aerosols (pollutants), larger involves aerosols (pollutants), larger
than gas molecules
than gas molecules
– equally effective across visible spectrumequally effective across visible spectrum
– explains hazy, gray daysexplains hazy, gray days
– accentuates sunset/riseaccentuates sunset/rise
(e.g., in polluted areas)
(e.g., in polluted areas)
3)
3) Non-selective scatteringNon-selective scattering
–water droplets in cloudswater droplets in clouds
–act like lenses; scatter all wavelengths equallyact like lenses; scatter all wavelengths equally
–why clouds appear grey or whitewhy clouds appear grey or white
–explains rainbowsexplains rainbows when viewing rain
when viewing rain
in the distance (each
in the distance (each
wavelength bent awavelength bent a
different amount)different amount)
Why non-selective
scattering is
important
Transmission of Insolation
Transmission of Insolation
• Percentage of energy passing through atmosphere Percentage of energy passing through atmosphere and reaching surface
and reaching surface
• Amount of energy reaching Earth surface is function Amount of energy reaching Earth surface is function of atmospheric absorption, scatter, and reflection
of atmospheric absorption, scatter, and reflection
• Clear vs. hazy, cloudy daysClear vs. hazy, cloudy days
Before proceeding to the next section, answer the following prompt based on information from the previous slides.
W2L: Take one minute and answer
this statement:
“
“
As solar energy travels through the
As solar energy travels through the
atmosphere it ……….”
atmosphere it ……….”
What happens to it ???
• Annual variation in insolation is ~ 7%
• Insolation reaching top atmosphere can be:
• transmittedtransmitted
• absorbedabsorbed (atmosphere and surface)
• scattered/reflectedscattered/reflected back to space
• Assume 100 units (100%) of insolation
reaches the top of the atmosphere …………
Now What?
Fate of Solar Energy
Fate of Solar Energy
Earth’s Solar (“Shortwave”) Radiation Earth’s Solar (“Shortwave”) Radiation
Balance: Balance:
100% sunlight in at top of atmosphere
19 + 45 + 25 + 6 + 5 =
100%
Q: If Earth’s surface absorbs 45% - why doesn’t it become extremely hot over
Answer – Other types of energy transfer also Answer – Other types of energy transfer also
occur: occur:
1.
1. Longwave Radiation TransferLongwave Radiation Transfer
(mainly between Earth & the atmosphere)
• Sun heats earth surface, Earth emits radiation
• Called “LongwaveLongwave” because much longer wavelength than radiation emitted by Sun due to cooler temp of earth (wavelength is dependent on temperature)
2. “Sensible”Sensible Heat Transfer (temperature
increases). Heat you can “sense” or feel. (due to temperature gradients from hot to cold)
3. “Latent”Latent Heat Transfer (temperature does not change)
(phase change evaporation, melting)
Longwave Radiation Transfer
So, net surface loss due to longwave = 16%
But there is an excess of 45% of solar radiation. Thus, we still have 45% -16% = 29% excess radiation at the surface of the Earth ………..… how do we get rid of
Answer:
Answer: “Sensible”“Sensible” and and “Latent”“Latent” heat heat transfers.
transfers.
Conduction
Conduction
– This is how excess heat This is how excess heat
energy in the surface of the
energy in the surface of the
Earth is transferred to the
Earth is transferred to the
atmosphere via an
atmosphere via an
extremely thin layer of air in
extremely thin layer of air in
contact with the surface
contact with the surface
Convection
Convection
– Once the heat energy is Once the heat energy is
transferred from the surface
transferred from the surface
to the air via conduction,
to the air via conduction,
convection takes over from
convection takes over from
here via “
here via “sensiblesensible” and ” and “
“latentlatent” heat transfers” heat transfers
First, recall two other methods of energy
First, recall two other methods of energy
transfer
transfer in addition to radiationin addition to radiation::
On the Molecular Level
On the Molecular Level
•
We have learned previously that when We have learned previously that when molecules absorb heat energy, they willmolecules absorb heat energy, they will
start to move faster (increased kinetic
start to move faster (increased kinetic
energy) and thus raising the temperature.
energy) and thus raising the temperature.
•
When the molecules have reached a When the molecules have reached acertain speed (temperature), the energy
certain speed (temperature), the energy
that they absorb will now be used to
that they absorb will now be used to
break the attractive forces (bonds)
break the attractive forces (bonds)
between them.
between them.
On a Molecular Level
On a Molecular Level
•
When the energy absorbed is used to break When the energy absorbed is used to break the attractive forces between them, therethe attractive forces between them, there
is
is no increase in speed of the molecule no increase in speed of the molecule (and thus no increase in temperature)
(and thus no increase in temperature)..
•
Which means the absorbed energy can only Which means the absorbed energy can only be used forbe used for ONLY ONE PURPOSEONLY ONE PURPOSE: : 1) To break attractive forces OR
1) To break attractive forces OR
2) Increase in speed of the molecules.
2) Increase in speed of the molecules.
•
Only one change is taking place at any Only one change is taking place at any time.time.
So what do we observe?
So what do we observe?
•
When the energy is used to increase the When the energy is used to increase the speed of the molecule, we see a rise inspeed of the molecule, we see a rise in
temperature of the substance called:
temperature of the substance called:
SENSIBLE HEAT
SENSIBLE HEAT
•
When the energy is used to break When the energy is used to breakattractive forces between molecules, we
attractive forces between molecules, we
see the substance changing in state.
see the substance changing in state.
This energy which brings about a
This energy which brings about a
change in state is known as:
change in state is known as:
LATENT HEAT
LATENT HEAT
Before proceeding to the next section, answer the following prompt based on information from the previous slides.
W2L: Take one minute and answer
this statement:
“
“
The difference between sensible heat
The difference between sensible heat
and latent heat is ……….”
and latent heat is ……….”
Changes in State
Changes in State
(vaporization)
Changes in State
Changes in State
Melting
Boiling
CONDENSATION SOLIDIFICATION (freezing) SolidGa
s
LiquidLoss of heat
Loss of heat
to the
to the
“system”
“system”
Gain of heat
Gain of heat
to the
to the
“system”
“system”
MELTING AND
MELTING AND
SOLIDIFICATION
SOLIDIFICATION
• When a When a solid changes to a liquidsolid changes to a liquid on heating, on heating, we call it
we call it melting. melting. In this instance, heat is In this instance, heat is ABSORBED
ABSORBED by the substance by the substance
• When a When a liquid changes to a solidliquid changes to a solid on cooling, on cooling, we call it
we call it solidification (freezing). solidification (freezing). In this In this instance, heat is
instance, heat is LOSTLOST by the substanceby the substance
MELTING AND
MELTING AND
SOLIDIFICATION
SOLIDIFICATION
•
In both cases, the heat that is absorbed In both cases, the heat that is absorbed or lost is known as theor lost is known as the latent heat of latent heat of fusion.
fusion.
•
When this latent heat is absorbed or When this latent heat is absorbed orlost, there is no change in temperature. lost, there is no change in temperature.
•
This means when a substance is This means when a substance is undergoing a change in state, the undergoing a change in state, the temperature will remain constant. temperature will remain constant.(vaporization)
Latent Heat of Fusion
Latent Heat of Fusion
“Latent Heat of Fusion”
Changes in State
Changes in State
melting
Boiling
CONDENSATION SolidGa
s
LiquidGain of heat
Gain of heat
to the
to the
“system”
“system”
Loss of heat
Loss of heat
Boiling and
Boiling and
Condensation
Condensation
•
When a When a liquid changes to a gasliquid changes to a gas on on heating, we call itheating, we call it boilingboiling. . In this In this instance, heat is
instance, heat is ABSORBEDABSORBED by the by the substance
substance
•
When a When a gas changes to a liquidgas changes to a liquid on on cooling, we call itcooling, we call it condensationcondensation. In this . In this instance, heat is
instance, heat is LOSTLOST by the substance by the substance
Vapor
Boiling and
Boiling and
Condensation
Condensation
•
The heat that is absorbed is known The heat that is absorbed is known as theas the latent heat of vaporizationlatent heat of vaporization..
•
The heat that is released is known as The heat that is released is known as thethe latent heat of condensationlatent heat of condensation..
•
When this latent heat is absorbed or When this latent heat is absorbed or lost, there is no change inlost, there is no change in
temperature.
temperature.
•
This means when a substance is This means when a substance is undergoing a change in state, theundergoing a change in state, the
temperature will remain constant.
(vaporization)
Latent Heat of
Latent Heat of
Vaporization/Condensation
Vaporization/Condensation
“Latent Heat of Vaporization”
“Latent Heat of Fusion” “Latent Heat of Condensation”
Latent Heat of Sublimation/Desublimation
Latent Heat of Sublimation/Desublimation
SUBLIMATION
SUBLIMATION: a transition from the solid to gas
phase with no intermediate liquid stage.
DESUBLIMATION
DESUBLIMATION: a transition from the gas to a
Sublimation
Sublimation
•
Glaciers in polar Glaciers in polar regions canregions can
experience a loss of
experience a loss of
water due to this
water due to this
process even when
process even when
there isn't enough
there isn't enough
energy to lose water
energy to lose water
mass from
mass from
evaporation
evaporation
Does sublimation absorb or release
•
Desublimation Desublimation is the is the process by which, inprocess by which, in
sub-freezing air,
sub-freezing air,
water vapor changes
water vapor changes
directly to ice without
directly to ice without
first becoming a
first becoming a
liquid. This is how
liquid. This is how
snow forms in clouds,
snow forms in clouds,
as well as frost on the
as well as frost on the
ground.
ground.
Does desublimation absorb or release energy?
Desublimation
Desublimation
(vaporization) “ “De subl imat ion” Desu blim atio n”
Latent Heat of
Latent Heat of
Sensible Heat
Sensible Heat
• Heat energy which is readily detected by your Heat energy which is readily detected by your senses
senses
• Magnitude is related to an object’s Magnitude is related to an object’s specific heatspecific heat
– The amount of energy needed to change the The amount of energy needed to change the
temperature of an object
temperature of an object
• Also related to massAlso related to mass
– Higher mass requires more energy for heatingHigher mass requires more energy for heating
• Sensible heat transfer occurs from Sensible heat transfer occurs from warmerwarmer to to cooler
cooler areas (i.e. from ground upward or from areas (i.e. from ground upward or from the equator to the poles)
the equator to the poles)
• Globally, Globally, 8 units of energy8 units of energy are transferred to the are transferred to the atmosphere as
atmosphere as sensible heatsensible heat
Latent Heat
Latent Heat
• Energy required to induce changes of state in a substanceEnergy required to induce changes of state in a substance
• In atmospheric processes, invariably involves waterIn atmospheric processes, invariably involves water
• When water is present, When water is present, latent heat of evaporationlatent heat of evaporation redirects some redirects some energy which would be used for sensible heat
energy which would be used for sensible heat
– Wet environments are cooler relative to their insolation amountsWet environments are cooler relative to their insolation amounts
• Latent heat of evaporationLatent heat of evaporation is stored in water vapor is stored in water vapor
– Released as latent heat of condensation when that change of Released as latent heat of condensation when that change of state is induced
state is induced
• Latent heat transfer occurs from regions of wetter-to-drierLatent heat transfer occurs from regions of wetter-to-drier
• Globally, Globally, 21 units of energy21 units of energy are transferred to the atmosphere as are transferred to the atmosphere as latent heat
latent heat
Heat Energy for Storms
Heat Energy for Storms
Latent heat released from the billions of vapor
Latent heat released from the billions of vapor
droplets during condensation and cloud
droplets during condensation and cloud
formation fuels storm energy needs, warms the
formation fuels storm energy needs, warms the
air, and encourages taller cloud growth.
Understanding Latent Heat:
Understanding Latent Heat:
Phase change requires an
Phase change requires an
release or absorption of
release or absorption of
energy!
energy!
•Latent heat of evaporation
• Latent heat of condensation
• Energy is:Energy is:
absorbed S
absorbed S L L
G
G
released G
released G L L
S
S
Remember all of that “excess”
Remember all of that “excess”
energy?
energy?
Longwave Radiation TransferSo net surface loss due to longwave = 16%
But there was an excess of 45% of solar radiation. Thus, we still have 45% -16% = 29% excess radiation at the surface … how do we get rid of it?
Summary : Total Energy
Summary : Total Energy
Balance
Balance
SW + LW + SH + LH = 0 for:
CONCEPTS
CONCEPTS
•
Fate of solar radiation Fate of solar radiation(absorption, scattering, transmission)
(absorption, scattering, transmission)
•
Earth’s energy balance Earth’s energy balance(SW + LW + SH + LH)
(SW + LW + SH + LH)
WHY ALL OF THIS
WHY ALL OF THIS
CONCERN ABOUT
CONCERN ABOUT
HEAT AND
HEAT AND
ENERGY?
ENERGY?
There is an imbalance of net radiation at
surface:
Equator/Tropics vs.
high latitudes
•
drives global air circulation•
agents: wind,ocean currents, weather systems
Variations in Net Radiation
Variations in Net Radiation
(ENERGY)
(ENERGY)
Tropic – to-tropic = energy surplus
Tropic – to-tropic = energy surplus
poles = energy deficits
poles = energy deficits