Unit 2 topic 1

• Diurnal energy budget


  The amount of energy entering a system, the amount leaving the system, and the energy transfer within the system
• Factors affecting the diurnal energy budget


  • Incoming (shortwave) solar radiation
  • Reflected solar radiation
  • Energy absorbed into the surface and subsurface
  • Albedo
  • Sensible heat transfer
  • Longwave radiation
  • Latent heat transfer – evaporation, dew and absorbed energy returned to Earth
• We live at the bottom of an invisible ocean called the atmosphere, a layer of gases surrounding our planet
• Gases in dry air


  • Nitrogen
  • Oxygen
  • Argon
  • Carbon dioxide
  • Helium
  • Neon
• Water vapour and dust are also part of Earth's atmosphere
• The atmosphere acts as a gigantic filter, keeping out most ultraviolet radiation while letting in the Sun's warming rays
• Ultraviolet radiation is harmful to living things and is what causes sunburns
• Solar heat is necessary for all life on Earth
• Layers of the atmosphere


  • Troposphere
  • Stratosphere
  • Mesosphere
  • Thermosphere
  • Exosphere
  • Ionosphere
• Troposphere


  • Lowest atmospheric layer
  • Almost all weather develops in the troposphere because it contains almost all of the atmosphere's water vapour
  • Air in the troposphere thins as altitude increases
  • Solar heat penetrates the troposphere easily
  • Absorbs heat reflected back from the ground in a process called the greenhouse effect
• Stratosphere


  • Calm with strong horizontal winds
  • Very dry with rare clouds
  • Contains ozone which prevents harmful UV rays from reaching Earth
• Mesosphere


  • Coldest temperatures in the atmosphere, dipping as low as -120 degrees Celsius
  • Highest clouds in the atmosphere
• Ionosphere


  • Reflects particles from solar wind
  • Conducts electricity and creates auroras
• Thermosphere


  • Thickest layer in the atmosphere
  • Contains mostly oxygen, helium, and hydrogen
  • Absorbs X-rays and ultraviolet radiation, propelling molecules to high speeds and temperatures
  • Despite high temperatures, there is little heat transfer due to low pressure
• Energy budget


  The amount of energy entering a system, the amount leaving the system, and the energy transfer within the system
• Components of the global energy budget


  • Incoming solar radiation (insolation)
  • Reflected by clouds
  • Reflected by surface (albedo)
  • Absorbed by atmospheric gases
  • Absorbed by clouds
  • Absorbed by Earth's surface
  • Outgoing longwave radiation
  • Latent heat transfer (evaporation and condensation)
• Factors controlling the amount of incoming solar radiation the Earth receives


  • Solar constant (energy released by the Sun)
  • Distance from the Sun
  • Angle of incidence of insolation
  • Length of day and night
• Local daytime energy budget


  1. Reflected solar radiation

  2. Longwave radiation

  3. Evaporation using energy from the surface

  4. Sensible heat transfer

  5. Heat transfer into the soil
• Albedo


  The reflectivity of a surface, expressed as a percentage
• ted


  Solar radiation
• Solar radiation


  Long-wave radiation
• Evaporation


  Using energy from the surface
• Sensible heat transfer


  1. Grass-covered surface

  2. Heat transfer into the soil (surface absorption)
• As the radiation from the Sun passes through the atmosphere, some is absorbed by liquids, gases and solids. Some is reflected and scattered, especially by the tops of clouds.
• A high albedo means the surface reflects most of the radiation that hits it and absorbs the rest. A low albedo means a surface reflects a small amount of the incoming radiation and absorbs the rest.
• Albedo examples


  • Fresh snow reflects up to 95 per cent
  • Dark surfaces have a low albedo
  • Light surfaces have a high albedo
  • Thin clouds reflect 30-40 per cent
  • Thicker clouds reflect 50-70 per cent
  • Towering cumulonimbus clouds can reflect up to 90 per cent
• Incoming solar radiation is converted into heat energy when it reaches the surface of the Earth.
• Incoming solar radiation exceeds outgoing heat energy for many hours after noon, and equilibrium is usually reached in mid-afternoon, from 3-5 p.m.
• Factors affecting energy absorbed by surface and subsurface


  • Presence of large bodies of water
  • Snow cover
  • Conduction will transfer some incoming energy from the surface into the sub-surface soil and rocks
• Light-coloured soil or rock


  Poor conductor, so heating will mainly be confined to the surface
• Dark volcanic soil or dark rocks

  Low albedos of 5-10 per cent, will absorb heat well
• Moisture content of sub-surface soil


  Affects its ability to conduct heat
• Coarse sandy soil with large pore spaces


  Poor conductor of heat, so the heat will concentrate on the surface
• Soil with high water content


  Conducts heat down into the sub-surface, so surface will be cooler
• Wind


  • Can remove heat quickly from a land surface
• Cloud cover and water vapour in the atmosphere


  • Affect the amount of reflection of incoming radiation and the amount that reaches the surface and sub-surface
• Long wave radiation


  Radiation emitted by the Earth's surface as it warms up, at a longer wavelength than incoming solar radiation
• 94 per cent of long wave radiation is absorbed by greenhouse gases in the atmosphere, warming the atmosphere and producing the natural greenhouse effect. The remaining 6 per cent is lost to space.
• Sensible heat transfer


  The energy required to change the temperature of a substance with no phase change
• Latent heat transfers


  The energy absorbed by or released from a substance during a phase change from a gas to a liquid or a solid or vice versa