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'
  

  
  

  
  

• E_Å
  is the solar energy at 1 AU ("constant")
  
• 1 AU = 1.5.10⁸ km = 1.5.10¹¹ m
  
• E_Å
  = L_ʘ/( 4.pR_p²) = L_ʘ/( 4.p1 AU)²)
  
• = 1.38.10³ W m^-2
  
• L_ʘ
  = E_Å
  4.p(1 AU)²
  
• E(Rp) = L_ʘ/( 4.pRp²) = E_Å
  /(Rp/1 AU)²
  
• = E_Å
  /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
  
• T_eff = effective temperature
  
• Earth, rp 1AU
  
• Albedo = .3 ( i.e. 70% of energy absorbed)
  
  • T_eff = 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,CF₂Cl_2, 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

•