1 GEOS 110 Winter 2011 Earth’s Surface Energy Balance 1.Energy Balance and Temperature a.Atmospheric influences on insolation: absorption, reflection, and scattering b.What happens to incoming solar radiation? (global scale; local scale later) c.Surface-atmosphere energy transfer d.Greenhouse effect e.Temp. distributions

2 Radiation is the transfer of electromagnetic (EM) energy via an electrical wave and a magnetic wave. When this energy is absorbed by an object there is an increase in molecular motion and hence in temperature. Radiation

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4 Sun: T~6000K E~7.4 x10 7 W/m 2, max  0.44  m Earth: T~300K E~ 460 W/m 2, max  9.66  m

5 Radiation Laws 1. All objects, at whatever temperature, emit radiant energy. 2. Hotter objects radiate more total energy per unit area than colder objects. E =  T 4 (Stefan-Boltzman Law)  =5.67e-8 Wm 2 K The hotter the body the shorter wavelength of maximum radiation max  = c / T(K) (Wein’s Law) c=2897  mK 4. Objects that are good absorbers of radiation are also good emitters. A perfect absorber/emitter is called a blackbody.

6 Insolation What happens to incoming solar radiation (=insolation)? It is absorbed, reflected, and scattered.

7 b. What happens to Solar Insolation? The global energy budget = a balance between incoming solar radiation (+) and outgoing terrestrial radiation (-)

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9 Absorption:  Reduces energy reaching Earth surface – different gases absorb different wavelengths of radiation Scattering:  Radiation is redirected

Scattering Gas molecules in the atmosphere scatter incoming solar radiation in all directions, not just back into space The smaller molecules scatter shorter wavelength, blue light. Gases and aerosols are more effective scattering different wavelengths:  Gas molecules are most effective scattering shorter wavelengths of visual light (i.e. blue and violet),  Aerosols scatter all wavelengths MoonriseEarthrise

11 b. What happens to Solar Insolation? On Average 50% does not reach surface: 225% absorbed by atmosphere (7% via ozone) 119% reflected via clouds 66% back scattered via atmosphere 50% that reaches the surface: 445% absorbed by Earth surface 55% reflected by ground If we assume a constant supply of incoming solar radiation:

12 b. The Fate of Solar Insolation planetary albedo = 30% (Average reflectivity) Earth and Atmosphere absorb 45% + 25% = 70% of solar insolation

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14 Earth’s Energy Balance 1.Energy Balance and Temperature a.Atmospheric influences on insolation: absorption, reflection, and scattering b.Fate of incoming solar radiation c.Surface-atmosphere energy transfer d.Greenhouse effect e.Temp. distributions

C. Surface – Atmosphere Energy Transfer Radiation Exchange: EEarth emits radiation (longwave), almost like a blackbody MMost of this radiation (96%) is absorbed by the atmosphere 15 (Radiation emitted by Earth) Radiation absorbed by atm.

C. Surface – Atmosphere Energy Transfer Radiation Exchange: Selective absorption 16 (Radiation emitted by Earth) Radiation absorbed by atm. Atmospheric “window”

C. Surface – Atmosphere Energy Transfer Radiation Exchange: Net loss of radiation

C. Surface – Atmosphere Energy Transfer 18 Net Radiation = absorption of insolation + net longwave radiation

C. Surface – Atmosphere Energy Transfer AAtmosphere = net radiation deficit SSurface = net radiation surplus Energy must transfer between the surface and the atmosphere CConduction: transfers radiant energy into Earth, and warms the laminar boundary layer ( = thin layer of air above surface) 19

Heat Transfer Mechanisms of Heat Transfer

C. Surface – Atmosphere Energy Transfer 21 Convection moves energy between surface and atmosphere: Free convection: Mixing related to differential buoyancy

C. Surface – Atmosphere Energy Transfer  Convection moves energy between surface and atmosphere: Forced convection: = disorganized flow 22 Hurricane Ike at landfall, Huston/Galveston, 13 Sep

C. Surface – Atmosphere Energy Transfer How does the surface energy surplus get to the atmosphere? 1. Sensible heat: RReadily detected heat energy MMagnitude of change related to object’s specific heat (J kg -1 K -1 ) and mass 2. Latent Heat: EEnergy required to change the phase of a substance 23

C. Surface – Atmosphere Energy Transfer When radiation hits water (e.g., ocean, lake, moist soil, plants that can transpire), energy that could have gone to sensible heating is redirected to evaporate some water. Evaporation of water makes energy available to the atmosphere that otherwise would warm the surface, thus acting as an energy transfer mechanism. There is no net energy loss 24

C. Surface – Atmosphere Energy Transfer 25 Surface surplus offset by transfer of sensible heat(8 units) and latent heat (21 units) heat to atmosphere.

C. Surface – Atmosphere Energy Transfer 26 Latent heat (21 units) is a bigger factor than sensible heat (8 units):

C. Surface – Atmosphere Energy Transfer 27 Latitudinal variations:  Between 38°N and S = net energy surpluses  Poleward of 38 o = net energy deficits  Winter hemispheres - Net energy deficits poleward of 15 o

28 Earth’s Heat Budget

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30 Aerosols - Aerosol = liquid or solid particle suspended in the atmosphere. - Large quantity = concentration of 1000 / cm 3. (1 breath = 1000cm 3 = 1 million aerosols) - Tiny = micrometers = 1 millionth of a meter. Aerosols are formed by human and natural causes (e.g., sea salt from ocean waves; fine soil; smoke and soot from fires, vehicles, and aircraft; volcanic eruptions).

31 Sulfate particles produced from volcanic eruptions causes a cooling of the surface.

32 Earth's surface is 5 million kilometers further from the sun in Northern summer than in winter, indicating that seasonal warmth is controlled by more than solar proximity.

33 Seasons & Solar Intensity Solar intensity, defined as the energy per area, governs earth's seasonal changes. A sunlight beam that strikes at an angle is spread across a greater surface area, and is a less intense heat source than a beam impinging directly. A sunlight beam that strikes at an angle is spread across a greater surface area, and is a less intense heat source than a beam impinging directly.

34 Earth's annual energy balance between solar insolation and terrestrial infrared radiation is achieved locally at only two lines of latitude. A global balance is maintained by excess heat from the equatorial region transferring toward the poles. A global balance is maintained by excess heat from the equatorial region transferring toward the poles.

35 Northern hemisphere sunrises are in the southeast during winter, but in the northeast in summer. Summer noon time sun is also higher above the horizon than the winter sun. Summer noon time sun is also higher above the horizon than the winter sun. Local Solar Changes

C. Surface – Atmosphere Energy Transfer 36 Latitudinal variations:  Energy surplus at low latitudes is offset by advection (horizontal heat movement) of heat poleward by global wind (75%) and ocean (25%) currents Global Sea Surface Temperatures: Climatology:

C. Surface – Atmosphere Energy Transfer 37 Ocean currents: 1. Climate change could cause a shift in the position of some ocean currents, through a variety of mechanism. Can you identify any land regions where climate could be vulnerable to shifts in nearby currents? 2. Are there any localities whose climate could cool even if the average global temperature were to warm?

Daily Temp (NYC)

Gases in DRY AIR

Atmospheric Pressure and Altitude

Thermal Structure of the atmosphere Determined by energy source, density of layers and composition of layers

Daily path of the sun for a location at ? latitude

Effect of Sun’s angle of incidence

Annual variation in daily duration of available insolation

Relationship between mean monthly temperature and latitude

Continental effect and Marine effect