Climates of the World

• The Earth-atmosphere system receives energy from the sun (99.9%), the rest come from space (.01%) and geothermal
• Convection


  Bulk transfer of energy by a fluid (Liquid or Gas)
• Conduction


  Energy transfer by contact (hot to cold) (ground heats the first 6 inches or 15 cm of atmosphere)
• Radiation


  Energy transfer that does not need a medium (sun heats earth's surface)
• Energy leaves the atmosphere in the form of infrared energy
• Solar energy entering the atmosphere heats the earth's surface (contact point), and then is transferred into the atmosphere and other parts of the climate system
• Climate science looks at climate and climate change primarily as a radiative problem
• Forms of energy


  • Radiative
  • Potential energy
  • Internal energy
  • Kinetic energy
  • Latent heating
  • Oceanic heat transport
• Total potential energy is the sum of radiative, potential, internal, and kinetic energy (Margules, 1903)
• The general circulation has the same time scale as large-scale meteorology and large-scale climate, time-scale is 15+ days to 10 years
• The sun generates potential energy, some of this (available potential energy) is converted in kinetic energy by cyclones and anticyclones (Eddies)
• The kinetic energy is then dissipated by friction
• Incoming solar radiation decreases from equator to pole
• Outgoing radiation is strongest at pole and falls off slower than incoming to the pole
• There is an energy surplus in the tropics, balance around 35º N latitude and deficit in the polar regions
• The surplus approximately equals the deficit
• There needs to be an equilibrium (2nd Law of Thermodynamics), so we get a transfer of energy from hot (source) equator to cold (sink) pole, involving cyclones and anticyclones
• Electromagnetic spectrum


  • X-Ray 0.01 microns
  • Ultraviolet .1
  • Visible. 4 microns
  • Near Infrared >1-8 microns
  • Microwave
  • Radio
• The output of energy by the sun is about 3.9x10^26 Watts (J/s)
• Flux density


  Energy per unit surface area
• The flux density on the sun's surface is 6.34x10^7 W/m^2
• The Earth intercepts only one 2-billionth of the sun's energy, resulting in a solar constant of ~1370 W/m^2
• Solar luminosity


  Flux density of radiant energy from the sun that falls on a unit area held normal to the direction of the sun just outside the earth's atmosphere
• Solar luminosity varies as the cosine of the zenith angle
• A nuclear weapon releases 6 x 10^13 J over about 3m, and this is released in about 0.3 microseconds (~6 x 10^11 W/m^2)
• Sunspots can cause a slight energy surplus for the Earth, which may have contributed to the little ice age (with constant CO2 of 280 PPM)
• Black body


  A coherent mass of material (such as a surface or collection of molecules) which have the attribute that all radiation incident is absorbed
• Radiation emitted by a black body is the maximum possible by a real body at that temperature (e.g. stars)
• Most of the light directed at a star is absorbed. It is therefore capable of absorbing all wavelengths of electromagnetic radiation, so is also capable of emitting all wavelengths of electromagnetic radiation
• Emissivity


  Absorptivity=100% for a Black Body (Kirschoff's law)
• Wien's law


  Wavelength (maximum)= 2897 / T (T in Kelvin)
• Solar radiation is concentrated more toward the visible and near infrared spectrum, where radiation emitted by planets tends to be long infrared
• Infrared radiation is lost to space (this is what heats the atmosphere)
• Stefan-Boltzmann's law


  Energy emitted by a blackbody is proportional to T^4
• If the surface of the sun emitted as a black body then its temperature would be 5783K
• The effective black body temperature of the Earth is 255K
• The Earth is not a perfect black body, so we need to take into account absorptance, emittance, and transmittance
• Radiative properties

  • Reflectance (Albedo)
  • Absorptance
  • Transmittance
  • Emittance
• For the atmosphere, Reflectance + Absorptance + Transmittance = 1
• The solar radiation budget involves reflection, absorption, and transmittance, with 30% being reflected (albedo)