Presentation on theme: "Earth’s Global Energy Balance Overview"— Presentation transcript:
1 Earth’s Global Energy Balance Overview Electromagnetic RadiationRadiation and temperatureSolar RadiationLongwave radiation from the EarthGlobal radiation balanceGeographic Variations in Energy FlowInsolation over the globeNet radiation, latitude and energy balanceSensible and latent heat transfer
2 Overview The global energy system Solar energy losses in the atmosphereAlbedoCounterradiation and the greenhouse effectGlobal energy budgets of the atmosphere & surfaceClimate & global change
3 What is light?Newton showed that white light is composed of all the colors of the rainbow.
4 Light is an Electromagnetic Wave & a Particle Photons: “pieces” of light, each with precise wavelength, frequency, and energy.Our eyes recognize frequency (or wavelength) as color!Use this slide to define wavelength, frequency, speed of light.
5 Photons Photons – are little packets of energy. The energy carried by each photon depends on its frequency (color)Blue light carries more energy per photon than red light.
10 Solar Radiation Shortwave Radiation from Sun (dark purple) Absorption of UV by O3Absorption by CO2 and water vapor (H2O↑) shown as valleysLongwave Radiation fromEarth (dark red)Much absorbed by CO2 & H2O↑
11 Scattering Solar radiation can be scattered by atmosphere Deflected off a molecule, cloud droplet, or particleMay go up toward space, or down toward EarthScattering most prevalent in blue wavelengthsThus, clear, blue skiesSome solar radiation goes directly to surfaceCalled transmissionSolar radiation arrives as 0.3μm to 3μm wavelengthsThis is shortwave radiation
13 Geographic Variation in Solar Energy Insolation – Incoming solar radiationMore intense where sun angle is highestLess intense with lower sun angleSame energy spread over a larger area
14 Insolation Daily insolation – avg radiation total in 24 hours Depends on :Sun angle – higher sun angle → greater insolationLength of day – higher latitudes get long summer daysAnnual insolation – avg radiation total for yearAlso depends on sun angle and length of dayBoth of these determined by latitudeSo, latitude determines annual insolation
15 Net Radiation Energy not usually balanced at any location Net Radiation - Difference between incoming and outgoing radiationBetween 40°N and 40°S, incoming > outgoingCreates energy surplusPoleward of 40°N & S, outgoing > incomingCreates energy deficitDeficit = Surplus, so net radiation for Earth = 0
16 Poleward Heat Transport Surplus energy moves toward poles (deficit regions)Carried by:Warm, moist airWarm sea waterTropical cyclonesPoleward heat transport is driving force behind:Global atmospheric circulationWeather systemsOcean currents
17 Why are there seasons? The Earth is tilted 23.5° from it orbital plane Combine tilt with orbitNorthern hemisphere gets more direct Sun part of year (northern summer)Southern hemisphere gets more direct Sun part of year (northern winter)Tilt & orbit create seasons, not distance to Sun
21 Path of the Sun in the Sky 40° NorthJune solstice:Sun rises north of east & sets north of westPeaks at 73.5° above horizon at noon15 hours of daylightHighest daily insolation of year
22 Path of the Sun in the Sky (40° North) DateNoon Sun AngleDaylightDailyInsolationJune Solstice73.5°15 hrs460 W/m2Dec. Solstice26.5°9 hrs160 W/m2Equinoxes50°12 hrs350 W/m2
23 Path of the Sun in the Sky (Equator) DateNoon Sun AngleDaylightDailyInsolationJune Solstice66.5°12 hrs~400 W/m2Dec. SolsticeEquinoxes90°440 W/m2
24 Path of the Sun in the Sky (North Pole) DateNoon Sun AngleDaylightDailyInsolationJune Solstice23.5°24 hrs500 W/m2Dec. SolsticeNo Sun0 hrs0 W/m2EquinoxesHorizon12 hrs~0 W/m2
25 Daily Insolation through the Year Yearly change in insolation greatest toward polesIn Arctic & Antarctic Circles, Sun is below horizon part of yearAt Equator, 2 maxs & 2 mins for daily insolationAt equinoxes & solsticesBetween tropics, also 2 maxs & 2 mins per yearYearly insolation change important to climateInsolation at equinox
26 Annual Insolation by Latitude Tilted Earth shown as red lineEquator greatest annual insolationConsiderable insolation at highest latitudesUntilted Earth (blue line)Highest latitudes little insolationBig changes in climateVery cold poleMassive poleward heat transport
27 Heat Transfer: Surplus energy is transported in two forms Sensible Heat – can be felt & measuredTransferred by conduction (touching surface)Transferred by convection (carried by rising air)Example: Moving air massesLatent Heat – cannot be felt or measuredStored as molecular motion when water changes phaseAbsorbed in evaporation, melting, and sublimationReleased in condensation, freezing, and depositionVery important form of heat transfer over long distancesExample: Storm systems, hurricanesConductionConvectionLatent heat absorbedin evaporation
28 Solar energy losses in the atmosphere Scattering due to:Gas moleculesDust or other particlesO2, O3, & H2O↑ most important absorbers of insolationGlobal avg – 49% of insolation makes it to surface
29 Once at the surface what happens? Albedo Proportion of shortwave radiation reflectedShown as a proportion (0-1)Examples:SnowfieldBlack pavement 0.03CloudsWater (calm, high angle 0.02), (low angle 0.80)Avg for Earth and atmosphere
30 So what happens to all the energy absorbed by these various processes? Counterradiation – heat absorbed by atmosphere reflected down to surfaceA – energy radiated to space from surfaceB – energy from surface absorbed by atmosphereC – energy radiated to space from atmosphereD – Counterradiation
31 Part of Counterradiation is the “Greenhouse Effect” Longwave radiation absorbed & re-radiated to surface by atmosphereLower atmosphere acts like blanket
32 Global Energy BudgetEnergy balanced for each level: surface, atmosphere, & space
33 Climate & Global Change Quantifying human impacts on climate difficultClimate and society have complex relationshipe.g., Industrial processesadd CO2 to atmosphere (warming)add aerosols to atmosphere (cooling)
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