Tuesday, January 15, 2008

EATS 1011 Lecture 4

  • In the northern hemisphere high pressure system goes clockwise, low pressure systems go counter-clockwise
    • This is due to the 'Coriolis effect'
  • GEOS bright colours represent 'cold'



  • EÅ
    is the solar energy at 1 AU ("constant")
  • 1 AU = 1.5.108 km = 1.5.1011 m
  • EÅ
    = Lʘ/( 4.pRp2) = Lʘ/( 4.p1 AU)2)
  • = 1.38.103 W m-2
  • Lʘ
    = EÅ
    4.p(1 AU)2
  • E(Rp) = Lʘ/( 4.pRp2) = EÅ
    /(Rp/1 AU)2
  • = EÅ
    /Rp2
  • Rp measured in AU


  • 37% of energy from the solar spectrum is near infrared


  • Most energy from the sun is less than 1 micron


  • We can see light where the sun outputs the most energy


  • The sun emits mostly in the UC, visible and near infrared regions


  • Humans can only see the visible region


  • The earth emits almost all in the mid infra red region


  • Satellites measuring IR can pick up differences in temperatures (clouds, water, surface, etc)


  • The area under the solar-radiation curve is the total (all wavelengths) solar radiance reaching the earth's orbit


    • =1.38*103 W m-2

Planetary Effective temperatures

  • The sun is far enough away to consider its rays parallel to eachother
  • Some light scatters back into space
  • The difference between infra red and solar energy is solar energy only comes through during the day
    • Emitted light as opposed to scattered
  • Albedo
    • A =
  • Radius of planet, b
  • Atmosphere emits as Planck body, sT4 W/m2
  • Steady state energy balance
    • Heating = cooling
  • Absorption (area*flux) = emission(area*flux)





  • Total amount of energy intercepted = π b2
  • Teff = effective temperature
  • Earth, rp 1AU
  • Albedo = .3 ( i.e. 70% of energy absorbed)
    • Teff = 255 Kelvin, = -18 Celcius
  • But The mean temperature is about 15 Celcius
    • T = 33 celcius
  • What is the implication for this temperature difference?
    • Natural greenhouse effect
      • Main greenhouse gas in the atmosphere is water vapour
  • Earth radiates / cools in the mid – IR (Wien's Law) from about 5km
  • Obliquity
    • the tilt of the planet from the sun

  • Mercury – rotates slowly and has a very large d/n temperature difference because heat deposited locally cannot be rapidly transferred to other locations such as the night side
  • Venus – T of 700k is actually the surface temperature and is evidence of a large greenhouse effect
  • Earth - natural greenhouse effect of about 33C
  • Mars - small greenhouse effect
  • Jupiter - interior heating - gravitational contraction
  • saturn - same
  • uranus - no
  • neptune - same as J and S
  • Pluto - aerosols and methane lead to a greenhouse effect

Heating of the Earth by Radiation

  • Solar radiation incident on atmosphere
    • Dilute 6000 K radiation
    • Scatters off air, clouds (numbers later)
    • Absorbed by aerosols, clouds, gases
    • Overall visible fairly transparent
    • Surface absorbs most radiation
      • Albedo trees(15%, ocean 10%)
    • Mid-IR radiation emitted from Earth / atmosphere system
    • Also called terrestrial radiation / long wavelength
    • Mid-IR is quite absorptive
    • "windows" 8-9, 10-12 чm
    • Main absorbers
      • H2O, CO2, clouds
    • Seconday absorbers
      • CH4, N2O, CFCI3,CF2Cl2, O3
    • Absorption of radiation
      • For graph on absorption
        • 100 = total absorption
        • 0 = no absorption
      • O2 and O3 absorb very energetic radiation from the sun
      • At about 9.6 microns ozone is acting as a greenhouse gas
    • Nitrous oxide
      • No role in visible spectrum
      • At about 4 microns and 6 microns absorbs quite a lot of energy
    • Methane
      • Heats the atmosphere a little bit
      • Plays a major role at about 6 microns
    • Water vapour
      • Water vapour absorbs a long range
        • Short mid and long range
        • From 4 -8 microns it plays a major rold
        • Plays a major role in controlling earths temperature
    • Carbon dioxide
      • Heats the atmosphere because it absorbs infrared radiation
      • Major band at about 15 microns
  • Most visible radiation goes to the surface

Transmission of solar and IR radiation


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