Warming the Warming the Earth and the Earth and the AtmosphereAtmosphere

Temperature and heat transferTemperature and heat transfer Balancing act - absorption, Balancing act - absorption,

emission and equilibriumemission and equilibrium Incoming solar energyIncoming solar energy

Temperature and Temperature and Heat TransferHeat Transfer

Temperature and Heat are NOT the same Temperature and Heat are NOT the same thing!thing!

•Temperature is the average kinetic energy of a group of Temperature is the average kinetic energy of a group of particles (atoms or molecules).particles (atoms or molecules).

•Heat is a quantity of energy.Heat is a quantity of energy.

•““Heating” is sometimes used to denote a change in Heating” is sometimes used to denote a change in temperature – NOT IN GES 241! Adding or subtracting a temperature – NOT IN GES 241! Adding or subtracting a quantity of heat energy may OR MAY NOT result in a quantity of heat energy may OR MAY NOT result in a temperature change.temperature change.

Temperature ScalesTemperature Scales

kinetic energy, temperature and kinetic energy, temperature and heatheat

Kelvin scaleKelvin scale Celsius scaleCelsius scale Fahrenheit scaleFahrenheit scale temperature conversionstemperature conversions

• Every temperature scale has two physically-meaningfulEvery temperature scale has two physically-meaningfulcharacteristics: a zero point and a degree interval.characteristics: a zero point and a degree interval.

Fig. 2-2, p. 27

Temperature as Average Temperature as Average Kinetic EnergyKinetic Energy

Atoms/molecules have mass and move at some Atoms/molecules have mass and move at some speed, thus have kinetic energy: speed, thus have kinetic energy:

KE = ½ mvKE = ½ mv22

Too many particles to keep track of all those Too many particles to keep track of all those individual kinetic energies (one for each particle)individual kinetic energies (one for each particle)

Temperature is the average kinetic energy of all Temperature is the average kinetic energy of all the particles in a substancethe particles in a substance

Ideal Gas LawIdeal Gas Law

Ideal Gas LawIdeal Gas Law

p = ρR Tp = ρR Tp: gas pressurep: gas pressureT: gas temperatureT: gas temperatureρ: gas densityρ: gas density

R is a constant for any given R is a constant for any given mixture of gases but changes from mixture of gases but changes from gas to gas. For dry air, R = 287 J gas to gas. For dry air, R = 287 J kgkg-1 -1 KK-1-1

Phases of MatterPhases of Matter

Phases of MatterPhases of Matter

Phases and Pressure• Phase of a substance depends on both

temperature and pressure• Often more than one phase is present

Phase ChangesPhase Changes

• Ionization: Stripping of electrons, changing atoms into plasma

• Dissociation: Breaking of molecules into atoms

• Evaporation: Breaking of flexible chemical bonds, changing liquid into solid

• Melting: Breaking of rigid chemical bonds, changing solid into liquid

Latent Heat - The Hidden Latent Heat - The Hidden WarmthWarmth

phase changes and energy phase changes and energy exchangesexchanges

sensible heatsensible heat• Latent heat explains why your skin feels cold whenLatent heat explains why your skin feels cold whenyou step out of a warm shower, and why perspirationyou step out of a warm shower, and why perspirationis an effective way to cool your body.is an effective way to cool your body.

Fig. 2-3, p. 28Stepped Art

ConductionConduction

conduction and heat transferconduction and heat transfer good conductors and poor good conductors and poor

conductorsconductors• Why are feathers (down) used in winter parkas?Why are feathers (down) used in winter parkas?

ConvectionConvection

convection and heat transferconvection and heat transfer thermalsthermals

• Soaring birds, like hawks and falcons, are highlySoaring birds, like hawks and falcons, are highlyskilled at finding thermals.skilled at finding thermals.

RadiationRadiation

radiation and energy transferradiation and energy transfer electromagnetic waveselectromagnetic waves Wein’s lawWein’s law Stefan-Boltzmann lawStefan-Boltzmann law Selective absorption of radiation: Selective absorption of radiation:

Greenhous GasesGreenhous Gases

What is light?What is light?

Light can act either like a wave or Light can act either like a wave or like a particlelike a particle

Particles of light are called Particles of light are called photonsphotons

WavesWaves

A A wavewave is a is a pattern of pattern of motion that motion that can carry can carry energy energy without without carrying carrying matter along matter along with itwith it

Properties of WavesProperties of Waves

WavelengthWavelength (λ) is the distance between (λ) is the distance between two wave peakstwo wave peaks

FrequencyFrequency (ν) is the number of times per (ν) is the number of times per second that a wave vibrates up and downsecond that a wave vibrates up and down

Wave SpeedWave Speed (c) is the distance one point (c) is the distance one point on the wave travels in one secondon the wave travels in one second

c = λνc = λν

Light: Electromagnetic Light: Electromagnetic WavesWaves

A light wave is a vibration of electric and A light wave is a vibration of electric and magnetic fieldsmagnetic fields

Light interacts with charged particles Light interacts with charged particles through these electric and magnetic fieldsthrough these electric and magnetic fields

Wavelength and Wavelength and FrequencyFrequency

wavelength wavelength xx frequency = speed of light frequency = speed of light = constant= constant

Fig. 2-7, p. 32

RadiationRadiation

electromagnetic spectrumelectromagnetic spectrum ultraviolet radiationultraviolet radiation visible radiationvisible radiation infrared radiationinfrared radiation

• Moderate amounts of ultraviolet radiation gives Moderate amounts of ultraviolet radiation gives you a healthy-looking tan; excessive amounts give you a healthy-looking tan; excessive amounts give you skin cancer.you skin cancer.

The Concept of Flux

(Chalkboard Example)

Flux: the quantity passing through a unit area in a unit time

Example: Energy Flux in SI units.

Energy Flux = “the number of Joules of energy passing through 1 square meter in one second”

Units of Energy Flux: Js-1m-2 = Wm-2

Fig. 2-8, p. 34

Stefan-Boltzmann LawStefan-Boltzmann Law

““The hotter the object, the more it The hotter the object, the more it radiates.”radiates.”

F = σTF = σT44

F: energy flux from body at temperature T (units: F: energy flux from body at temperature T (units: WmWm-2-2))T: temperature of bodyT: temperature of bodyσ: Stefan-Boltzmann constant, σ=5.67x10σ: Stefan-Boltzmann constant, σ=5.67x10-8-8 Wm Wm-2-2KK-4-4

Stefan-Boltzmann LawStefan-Boltzmann Law

• Blackbody flux is the total area Blackbody flux is the total area under the curve.under the curve.

• Fourth power means hot objects Fourth power means hot objects are radiating MUCH more than cool are radiating MUCH more than cool onesones

Example: 2 objects, one at 300 K and one at 600 K. Example: 2 objects, one at 300 K and one at 600 K. One object is twice as hot, but it radiates 16 times One object is twice as hot, but it radiates 16 times the energy from each square meter of its surface the energy from each square meter of its surface than the cooler one.than the cooler one.

Fig. 2-9, p. 34

Wien’s LawWien’s Law““The hotter the object, the shorter The hotter the object, the shorter wavelength light it emits.”wavelength light it emits.”

λλmaxmax = C / T = C / T

λλmaxmax: Wavelength of maximum blackbody emission : Wavelength of maximum blackbody emission (in microns/micrometers, (in microns/micrometers, μmμm))C: constant, C = 2898 C: constant, C = 2898 μmμm K KT: body temperature in KT: body temperature in K

Wien’s LawWien’s LawExample 1: Earth at 288 KExample 1: Earth at 288 K

λλmaxmax = 2898 = 2898 μmμm K / 288 K = 10 K / 288 K = 10 μmμm

10 microns is IR radiation. Earth radiates mostly 10 microns is IR radiation. Earth radiates mostly in the infrared.in the infrared.

Example 2: The Sun at 5778 KExample 2: The Sun at 5778 K

λλmaxmax = 2898 μm K / 5778 K = 0.501 μm = 501 nm = 2898 μm K / 5778 K = 0.501 μm = 501 nm

501 nm is visible (green) radiation. The Sun radiates mostly in 501 nm is visible (green) radiation. The Sun radiates mostly in the visible (green).the visible (green).

Balancing Act - Balancing Act - Absorption, Absorption,

Emission, and Emission, and EquilibriumEquilibrium

Selective Absorbers and Selective Absorbers and the Atmospheric the Atmospheric

Greenhouse EffectGreenhouse Effect blackbody radiationblackbody radiation selective absorbersselective absorbers atmospheric greenhouse effectatmospheric greenhouse effect

• The best greenhouse gas is water The best greenhouse gas is water vapor.vapor.

Particles of LightParticles of Light

Particles of light are called Particles of light are called photonsphotons Each photon has a wavelength and a Each photon has a wavelength and a

frequencyfrequency The energy of a photon depends on The energy of a photon depends on

its frequencyits frequency

Wavelength, Frequency, Wavelength, Frequency, and Energyand Energy

ν = ν = cc= wavelength ν= frequency= wavelength ν= frequency

cc = 3.00 = 3.00 xx 10 1088 ms ms-1-1 “speed of light” “speed of light”

E = h E = h ννphoton energyphoton energy

h h = 6.626 = 6.626 xx 10 10-34-34 J s J s

Atomic Analogy: Child’s Playslide

(Chalkboard)

Energy Level Energy Level TransitionsTransitions

The only The only allowed allowed changes in changes in energy are energy are those those corresponding corresponding to a transition to a transition between between energy levelsenergy levelsAllowedNot Allowed

(Hydrogen Atom)(Hydrogen Atom)

Chemical FingerprintsChemical Fingerprints

We can plot those energy transitions as frequencies We can plot those energy transitions as frequencies (because of E=hν ) and therefore as wavelengths (because of E=hν ) and therefore as wavelengths (because of c=λν)(because of c=λν)

Each type of atom has a unique spectral fingerprintEach type of atom has a unique spectral fingerprint

Energy Levels of Energy Levels of MoleculesMolecules

Molecules have additional energy levels Molecules have additional energy levels because they can vibrate and rotatebecause they can vibrate and rotate

Energy Levels of Energy Levels of MoleculesMolecules

The large numbers of vibrational and The large numbers of vibrational and rotational energy levels can make the rotational energy levels can make the spectra of molecules very complicatedspectra of molecules very complicated

Many of these molecular transitions are Many of these molecular transitions are in the infrared part of the spectrumin the infrared part of the spectrum

So how does the greenhouse effect work then…

1. Atmosphere contains gases that selectively absorb IR radiation, but transmit visible light (“greenhouse gases”)

2. Visible light (from the 5778 K Sun) travels through the atmosphere and is absorbed by the surface.

3. The surface (≈ 300 K) re-radiates that energy upward as IR light.

1. The IR energy gets absorbed by atmospheric GHGs.

2. The atmosphere radiates some upward to space, but also back downward to the surface. This energy raises the temperature of the ground.

The simplest greenhouse effect calculation you can do…

(Chalkboard)

The Global Energy Budget

Just like a bank budget:Bank: In = Out + SavingsEarth Energy: In = Out + Energy Storage

Energy can be stored in many ways, including temperature can change.

Working definition of weather: “Weather is the dynamical way in which the atmosphere maintains the long-term global energy balance.”

The Bathtub Analogy for Energy Balance

(Chalkboard)

Incoming Solar Incoming Solar EnergyEnergy

The Earth’s Annual The Earth’s Annual Energy BalanceEnergy Balance

What happens to the solar energy What happens to the solar energy that reaches the top of the earth’s that reaches the top of the earth’s atmosphere?atmosphere?

What happens to the solar energy What happens to the solar energy that is absorbed by the earth’s that is absorbed by the earth’s surface and by the atmosphere?surface and by the atmosphere?

Scattered and Reflected Scattered and Reflected LightLight

scatteringscattering reflectionreflection albedoalbedo

• Scattering is Scattering is responsible for the responsible for the blue sky color.blue sky color.

Fig. 2-15, p. 41

Fig. 2-16, p. 42

FIGURE 2.16 The earth-atmosphere energy balance. Numbers represent approximations based on surface observations and satellite data. While the actual value of each process may vary by several percent, it is the relative size of the numbers that is important. Stepped Art

Fig. 2-16, p. 42

Why the Earth has Why the Earth has SeasonsSeasons

earth-sun distanceearth-sun distance tilt of the earth’s axistilt of the earth’s axis

• Earth-sun Earth-sun distance has distance has little effect on little effect on atmospheric atmospheric temperature.temperature.

Seasons in the Northern Seasons in the Northern HemisphereHemisphere

insolationinsolation summer solsticesummer solstice spring and autumn equinoxspring and autumn equinox

Seasons in the Southern Seasons in the Southern HemisphereHemisphere

tilttilt solsticesolstice equinoxequinox

Local Seasonal Local Seasonal VariationsVariations

slope of hillsidesslope of hillsides vegetation differencesvegetation differences

• Homes can exploit Homes can exploit seasonal variations: seasonal variations: large windows large windows should face south.should face south.

Air TemperatureAir Temperature

Daily temperature variationsDaily temperature variations The controls of temperatureThe controls of temperature Air temperature dataAir temperature data Air temperature and human comfortAir temperature and human comfort Measuring air temperatureMeasuring air temperature

Daily Temperature Daily Temperature VariationsVariations

Daytime WarmingDaytime Warming

thermalsthermals forced convectionforced convection water vapor effectswater vapor effects

• Cumulus clouds are markers of convection.Cumulus clouds are markers of convection.

Nighttime CoolingNighttime Cooling

radiational coolingradiational cooling nocturnal inversionsnocturnal inversions

• Inversions tend to occur on clear, calm nights.Inversions tend to occur on clear, calm nights.

Fig. 3-1, p. 56

Stepped Art

Cold Air Near the Cold Air Near the SurfaceSurface

inversionsinversions thermal beltsthermal belts

• Drainage winds: cold air that slides downhill. Drainage winds: cold air that slides downhill.

The Controls of The Controls of TemperatureTemperature

latitudelatitude land and water distributionland and water distribution ocean currentsocean currents elevationelevation specific heatspecific heat

• Average weather conditions in the interior of large continents Average weather conditions in the interior of large continents are much different than average conditions in coastal areas.are much different than average conditions in coastal areas.

Daily, Monthly and Daily, Monthly and Yearly TemperaturesYearly Temperatures

diurnal temperature rangediurnal temperature range clouds and humidity effectsclouds and humidity effects proximity to large bodies of waterproximity to large bodies of water annual temperature rangeannual temperature range

• Clouds tend to reduce daytime temperatures, butClouds tend to reduce daytime temperatures, butincrease nighttime temperatures.increase nighttime temperatures.

Fig. 3-11, p. 65