Ch3: Energy Balance and Temperature

1. About the first in-class assignment

2. About reading the textbook

Review of Ch2Review of Ch2

– Know 3 methods of energy transferKnow 3 methods of energy transfer

– Know the names of the 6 wavelength Know the names of the 6 wavelength categories in the electromagnetic radiation categories in the electromagnetic radiation spectrumspectrum

– Know the wavelength range of Sun (shortwave) Know the wavelength range of Sun (shortwave) and Earth (longwave) raditionand Earth (longwave) radition

– Know the two basic motions of the EarthKnow the two basic motions of the Earth

– Know what causes the seasons: the Earth’s tilt Know what causes the seasons: the Earth’s tilt and the 3 ways it affects the solar insolationand the 3 ways it affects the solar insolation

Satellite Measurements of the Satellite Measurements of the Earth’s Radiation BudgetEarth’s Radiation Budget

NASA’s Earth Radiation Budget Satellite (ERBS) 1985-1989

Earth’s energy budget (averaged over Earth’s energy budget (averaged over the whole globe and over a long timethe whole globe and over a long time

• At the top of the atmosphere: At the top of the atmosphere: Incoming shortwave = Reflected Shortwave + Emitted longwaveIncoming shortwave = Reflected Shortwave + Emitted longwave• At the surface:At the surface: Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming) Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming) + Latent heat flux + sensible heat flux+ Latent heat flux + sensible heat flux

Sensible heat 7%

Latent heat 23%

Net Longwave 21%

Yellow: shortwave

Red: longwave

Atmospheric influences on Atmospheric influences on radiationradiation

Absorption Absorption (absorber (absorber warms)warms)

ReflectionReflection ScatteringScattering

Atmospheric Absorption - The Greenhouse EffectAtmospheric Absorption - The Greenhouse Effect

Transparent Transparent to solar to solar (shortwave) (shortwave) radiationradiation

Opaque to Opaque to earth’s earth’s (longwave) (longwave) radiationradiation

Major GH gases: CO2, H20(v), CH4

The wildcard: Clouds!The wildcard: Clouds! They (1) absorb just about all longwave, They (1) absorb just about all longwave,

and (2) reflect shortwave back to and (2) reflect shortwave back to spacespace

The unanswered questions The unanswered questions (challenges) in earth’s radiation (challenges) in earth’s radiation

budgetbudget

• How will the water vapor (HHow will the water vapor (H22O) change O) change associated with global warming? (Water associated with global warming? (Water vapor feedback problem)vapor feedback problem)

• How will the clouds change associated How will the clouds change associated with global warming? (Cloud-radiation with global warming? (Cloud-radiation feedback problem)feedback problem)

• How much do the clouds absorb shortwave How much do the clouds absorb shortwave radiation? (“Anomalous absorption” radiation? (“Anomalous absorption” problem)problem)

3 Types of Scattering: 3 Types of Scattering: 1.1. RaleighRaleigh

2.2. MieMie

3.3. Non-SelectiveNon-Selective

Atmospheric Atmospheric ScatteringScattering

A discussion of each type follows…A discussion of each type follows…

1) Rayleigh scattering• involves gases, smaller than 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

2) Mie scattering2) Mie scattering– involves aerosols, larger than gas moleculesinvolves aerosols, larger than gas molecules– forward scatterforward scatter– equally effective across visible spectrumequally effective across visible spectrum– explains hazy, gray daysexplains hazy, gray days

3) Non-selective scattering3) Non-selective scattering– water droplets in clouds (larger than gas molecules)water droplets in clouds (larger than gas molecules)– Act like lenses; scatter all wavelengths equallyAct like lenses; scatter all wavelengths equally– Explains rainbowsExplains rainbows

when viewing rainwhen viewing rainin the distance (each in the distance (each

wavelength bent awavelength bent a different amount)different amount)

Surface “Sensible” and Surface “Sensible” and “Latent” heat transfers“Latent” heat transfers

1.1. ConductionConduction– This is how excess heat in ground This is how excess heat in ground

is transferred to the atmosphere is transferred to the atmosphere via an extremely thin layer of air via an extremely thin layer of air in contact with the surfacein contact with the surface

2.2. ConvectionConvection– Once the heat is transferred from Once the heat is transferred from

the surface to the air via the surface to the air via conduction, convection takes over conduction, convection takes over from here via “sensible” and from here via “sensible” and “latent” heat transfers“latent” heat transfers

First, recall 2 other methods of First, recall 2 other methods of

energy transfer in addition to energy transfer in addition to radiation:radiation:

Sensible HeatSensible Heat • Heat energy which is readily detectedHeat energy which is readily detected

• Magnitude is related to an object’s specific Magnitude is related to an object’s specific heatheat– The amount of energy needed to change the The amount of energy needed to change the

temperature of an object a particular amount in temperature of an object a particular amount in J/kg/KJ/kg/K

• Related to massRelated to mass– Higher mass requires more energy for heatingHigher mass requires more energy for heating

• Sensible heat transfer occurs from warmer to Sensible heat transfer occurs from warmer to cooler areas (i.e., from ground upward)cooler areas (i.e., from ground upward)

Latent HeatLatent Heat• Energy required to induce changes of state Energy required to induce changes of state

in a substancein a substance

• In atmospheric processes, invariably In atmospheric processes, invariably involves waterinvolves water

• When water is present, latent heat of When water is present, latent heat of evaporation redirects some energy which evaporation redirects some energy which would be used for sensible heatwould be used for sensible heat– Wet environments are cooler relative to Wet environments are cooler relative to

their insolation amountstheir insolation amounts

• Latent heat of evaporation is stored in water Latent heat of evaporation is stored in water vaporvapor– Released as latent heat of condensation Released as latent heat of condensation

when that change of state is inducedwhen that change of state is induced

• Latent heat transfer occurs from regions of Latent heat transfer occurs from regions of wetter-to-drierwetter-to-drier

The unanswered questions The unanswered questions (challenges) in earth’s surface (challenges) in earth’s surface

fluxesfluxes• How large are the latent heat flux How large are the latent heat flux

(evaportranspiration) and sensible heat flux over (evaportranspiration) and sensible heat flux over land? How will they change with global warming? land? How will they change with global warming? (Land-atmospher feedback problem)(Land-atmospher feedback problem)

Net Radiation and Net Radiation and TemperatureTemperature• Earth’s radiation balance is a function of an Earth’s radiation balance is a function of an

incoming and outgoing radiation equilibrium incoming and outgoing radiation equilibrium (SW + LW = Net)(SW + LW = Net)

• If parameters were changed, a new If parameters were changed, a new equilibrium would be achievedequilibrium would be achieved

• Balances occur on an annual global scale and Balances occur on an annual global scale and diurnally over local spatial scalesdiurnally over local spatial scales

Daily/Seasonal

Radiation Patterns

• insolation peak vs. temperatureinsolation peak vs. temperature• daily lagdaily lag• seasonal lagseasonal lag•Lag is function of type of Lag is function of type of surface, wetness, wind, etcsurface, wetness, wind, etc

• Temperature increases whenTemperature increases when input > outputinput > output• Temperature decreases whenTemperature decreases when input < outputinput < output

• tropic-to-tropic – energy surplus• poles – energy deficits• ~ 38o N/S – balance

• imbalance of net radiation at surface Equator/Tropics vs. high latitudes

• drives global circulation• agents: wind, ocean currents, weather systems

Latitudinal Variations in Net Radiation

Seasonal variation of surface Seasonal variation of surface radiationradiation

Seasonal variation of surface energy Seasonal variation of surface energy budgetbudget

Storage change = net radiation - latent heat flux - sensible heat flux

Principal Controls on Temperature   Principal Controls on Temperature   

1.1. LatitudeLatitude

2.2. AltitudeAltitude

3.3. Atmospheric CirculationAtmospheric Circulation

4.4. Land-Water ContrastsLand-Water Contrasts

5.5. Ocean CurrentsOcean Currents

6.6. Local EffectsLocal Effects

Seasonal variation of surface air Seasonal variation of surface air temperaturetemperature

• T decreases poleward• larger T gradient in winter• isotherms shift seasonally• T over land > water in summer• NH steeper T gradient

Seasonal Seasonal Temp Temp DistributioDistributio

nsns

Temperature Ranges (Summer minus Winter)Large over land, small over ocean

ConceptConceptss• Earth’s energy balance at the top of the atmosphere Earth’s energy balance at the top of the atmosphere

and at the surface. What percentage of solar energy and at the surface. What percentage of solar energy is absorbed by the surface?is absorbed by the surface?

• Atmospheric influences on radiation (3 ways)Atmospheric influences on radiation (3 ways)

• What cause the greenhouse effect? What are the What cause the greenhouse effect? What are the major greenhouse gases? What is the “wildcard”?major greenhouse gases? What is the “wildcard”?

• The three types of atmospheric scattering. What The three types of atmospheric scattering. What causes the blue sky? Why causes the reddish-orange causes the blue sky? Why causes the reddish-orange sunsets? What causes the colors of rainbow?sunsets? What causes the colors of rainbow?

• Basic characteristics of global temperature Basic characteristics of global temperature distribution (T decreases poleward, isotherm shifts distribution (T decreases poleward, isotherm shifts seasonally, T over land > over ocean in summer).seasonally, T over land > over ocean in summer).

For Wednesday’s lectureFor Wednesday’s lecture• Catch up on reading if you haven’t (through Catch up on reading if you haven’t (through

Ch4)Ch4)