test 4

• Heat transfer

  • Conduction
  • Convection
  • Radiation and Radiation Budget
• Outline

  • Heat Transfer
  • Conduction
  • Convection
  • Radiation and Radiation Budget (part 1)
  • Radiant Energy (Radiation and Temperature, Radiation of the Sun and The earth)
  • Radiation: Absorption, Emission, and Equilibrium (Selective absorbers and the atmospheric greenhouse effects)
  • Enhancement of greenhouse effect
• Conduction

  The transfer of heat from one molecule to another molecule within a substance, usually from warmer to colder. The greater the temperature difference, the more rapid the heat transfer.
• Substances and their heat conductivity (Watts per meter per ºC)

  • Still air (0.023)
  • Wood (0.08)
  • Dry soil (0.25)
  • Water (0.60)
  • Snow (0.63)
  • Wet soil (2.1)
  • Ice (2.1)
  • Sandstone (2.6)
  • Granite (2.7)
  • Iron (80)
  • Silver (427)
• Heat conductivity describes a substance's ability to conduct heat as a consequence of molecular motion.
• A substance that can easily pass energy from one molecule to another is a good conductor of heat.
• Air is an extremely poor conductor of heat.
• In calm weather, the hot ground only warms a shallow layer of air a few cm thick by conduction.
• Convection

  The transfer of heat by the mass movement of a fluid (such as water and air)
• Convection in the atmosphere

  1. Air molecules adjacent to hot surfaces bounce against them, gaining extra energy by conduction

  2. The heated air expands and becomes less dense than the surrounding cooler air

  3. The expanded warm air is buoyed upward and rises
• Thermal

  A rising air bubble
• Air that rises

  Expands and cools
• Air that sinks

  Is compressed and warms
• Air parcel moves upward

  It is less dense than surrounding air
• Air pressure is low at the top of the atmosphere

  Molecules in air parcel will use their energy to move to fill the gap, expand and lose energy (heat)
• Colder air parcel moves downward

  It is heavier than surrounding air
• Air pressure is higher in the lower atmosphere

  Molecules bounce with each other more and move faster, increasing its kinetic energy (means temperature)
• Convective Circulation

  Convection is a movement of a thermal vertically, Advection is a movement of a thermal horizontally – usually assisted by wind.
• Radiant Energy

  The energy transferred from the Sun to your body/skin
• Radiant Energy travels in the form of waves, and since they have magnetic and electrical properties, they are called electromagnetic waves.
• Electromagnetic waves do not need molecules to propagate them.
• In a vacuum, electromagnetic waves travel at a constant speed of nearly 300,000 km (186,000 mi) per second—the speed of light.
• Sunlight warms your skin with little effect on the atmosphere.
• Insolation


  The amount of solar radiation reaching a given area.
• Scattering


  The process in which electromagnetic radiation or particles are deflected or diffused.
• Reflection


  The throwing back by a body or surface of light, heat, or sound without absorbing it.
• Emission


  The production and discharge of something, especially gas or radiation.
• As the wavelength decreases


  The energy carried per wave increases
• All things (whose temperature is above absolute zero), no matter how big or small, emit radiation.
• Each object has vibrating molecules that radiating a wide range of electromagnetic waves.
• The wavelengths of the radiation


  Depends on the body's temperature
• As the temperature of an object increases


  More total radiation is emitted each second
• Sun's surface temperature


  Nearly 6000 K (5726.85 ºC)
• Earth's surface temperature


  Around 288 K (15 ºC)
• The Sun radiates more energy than the Earth.
• Wien's law demonstrates that as the temperature of an object increases, the wavelength at which maximum emission occurs is shifted toward shorter values.
• Sun emits


  Shortwave radiation (solar radiation)
• Earth emits


  Longwave radiation (terrestrial radiation)
• Our eyes are sensitive to radiation between 0.4 and 0.7 μm, these waves reach the eye and stimulate the sensation of color (visible region).
• The color violet is the shortest wavelength of visible light, the longest wavelengths of visible light correspond to the color red.