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(1)

EARTH’S ENERGY BALANCE

EARTH’S ENERGY BALANCE

(Heat and Temperature)

(Heat and Temperature)

(2)

What happens to solar

radiation as it travels

through the atmosphere?

(3)

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

(4)

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 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. 

(6)

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

(7)

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

(8)

Sun Angle and Amount of Insolation

Sun Angle and Amount of Insolation

More direct energy  per unit area

Less direct energy  per unit area

(9)

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 ………...”

(10)

Global Energy Balance

Global Energy Balance

(11)

Atmospheric Influences on

Atmospheric Influences on

Insolation

Insolation

1.

1.AbsorptionAbsorption

2.

2.Reflection and ScatteringReflection and Scattering

3.

3.TransmissionTransmission

(12)

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

(13)

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

(14)

Reflection and Scattering

Reflection and Scattering

ReflectionReflection – redirection of energy without – redirection of energy without absorption

absorption

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)

(15)

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 the

scattering

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

(16)

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…

(17)

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?

(18)
(19)

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)

(20)

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)

(21)

Why non-selective 

scattering is 

important

(22)

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

(23)

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 ……….”

(24)

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

(25)

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

(26)

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)

(27)

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

(28)

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::

(29)

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 will

molecules 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 a

certain 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.

(30)

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, there

the 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 for

be 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.

(31)

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 in

speed 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 break

attractive 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

(32)

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 ……….”

(33)

Changes in State

Changes in State

(vaporization)

(34)

Changes in State

Changes in State

Melting

Boiling

CONDENSATION SOLIDIFICATION (freezing) Solid

Ga

s

Liquid

Loss of heat

Loss of heat

to the

to the

“system”

“system”

Gain of heat

Gain of heat

to the

to the

“system”

“system”

(35)

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

(36)

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 the

or 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 or

lost, 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.

(37)

(vaporization)

Latent Heat of Fusion

Latent Heat of Fusion

“Latent Heat of Fusion”

(38)

Changes in State

Changes in State

melting

Boiling

CONDENSATION Solid

Ga

s

Liquid

Gain of heat

Gain of heat

to the

to the

“system”

“system”

Loss of heat

Loss of heat

(39)

Boiling and

Boiling and

Condensation

Condensation

When a When a liquid changes to a gasliquid changes to a gas on on heating, we call it

heating, 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 it

cooling, we call it condensationcondensation. In this . In this instance, heat is

instance, heat is LOSTLOST by the substance by the substance

Vapor

(40)

Boiling and

Boiling and

Condensation

Condensation

The heat that is absorbed is known The heat that is absorbed is known as the

as the latent heat of vaporizationlatent heat of vaporization..

The heat that is released is known as The heat that is released is known as the

the 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 in

lost, there is no change in

temperature.

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.

(41)

(vaporization)

Latent Heat of

Latent Heat of

Vaporization/Condensation

Vaporization/Condensation

“Latent Heat of Vaporization”

“Latent Heat of Fusion” “Latent Heat of Condensation”

(42)

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

(43)

Sublimation

Sublimation

Glaciers in polar Glaciers in polar regions can

regions 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

(44)

Desublimation Desublimation is the is the process by which, in

process 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

(45)

(vaporization) “De subl imat ion” Desu blim atio n”

Latent Heat of

Latent Heat of

(46)

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

(47)

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

(48)

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.

(49)

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 Transfer

So 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?

(50)

Summary : Total Energy

Summary : Total Energy

Balance

Balance

SW + LW + SH + LH = 0 for:

(51)

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)

(52)

WHY ALL OF THIS

WHY ALL OF THIS

CONCERN ABOUT

CONCERN ABOUT

HEAT AND

HEAT AND

ENERGY?

ENERGY?

(53)

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

References

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