Skip to main content

Radiant Energy

Learning Objectives

  1. Explain how electromagnetic radiation works and explain the different types of radiant energy
  2. Describe the major components of the energy balance equation
  3. Explain the four forms of energy transfer and how they correspond to each component of the energy balance equation.
  4. Illustrate the direction (positive/negative) and relative magnitude of local energy exchanges during various seasons and at night/day.
  5. Explain how the presence or absence of vegetation affects the local energy balance and each of its energy components.
  6. Define with your own words, and put into context, all the terms in the glossary.

Electromagnetic radiation

  • Kinetic energy: Due to motion of an object
  • Chemical energy: As in gasoline, oil, coal, natural gas
  • Nuclear energy: As in nuclear reactor fuel
  • Radiant energy: As in sunlight
  • Heat energy: As in hot water, molten metal
  • Electircal energy: As in a light bulb, electric motor

Radiant energy

Most things are powered via the sun.

Can travel via vaccuum.

Can be simplified into shortwave and longwave radiation. * Shortwave radiation: Includes wavelengths in the near infrared, visible, and near ultraviolet sections. Mainly the sun. * Longwave radiation: Mostly in the infrared, longwave radiation is related to the emission of heat. Heat.

Solar Radiation: * Total solar irradiance (previously and erroneously called solar constant), is the average energy from the sun at the Earth's top of atmosphere, measured perpendicularly to the radiation.

Equations and components:

Energy Balance Equation

Day: QE = S + D - aK + L⤓ - L⤒ ± Lh ± Sh ± Ch Night: QE = L⤓ - L⤒ ± Lh ± Sh ± Ch

Terms

Direct solar radiation (S) Diffuse radiation (D) Incoming shortwave radiation / Insolation (K) = S + D Albedo (a) Outgoing shortwave radiation (aK, K⤒) Net shortwave radiation (K*) Incoming Longwave Radiation (L⤓) Outgoing Longwave Radiation (L⤒) Net Radiant Energy (R) Latent Heat Flux (Lh)

Forms of energy transfer

  • Radiative: emitted by objects with temperature > 0 K (All objects emit long-wave radiation, once it reaches a certain temperature, it might start releasing short-wave radiation) (K, Incoming / outcoming L)
  • Convection: Vertical mixing of fluids (S_(h))
  • Conduction: molecule to molecule contact (C_(h), S_(h))
  • Latent heat: energy absorbed or released during a phase change (L_(h)), when water evaporates or condenses

Component particularities

  • Albedo for different land uses

Latent Heat: * Energy consumed or released to change the temperature (vibration state) of water or another substance.

Sensible heat: * Molecules from hotter object in direct contact with colder object will transfer heat via conduction.

Local energy balance

  • A positive + sign during a spring day means heat gains for the snowpack, which is either increasing its temperature or melting.
  • A negative sign during a spring day means heat losses for the snowpack, which is either decreasing its temperature or refreezing.

[localenergybalancesoil.png] [localenergybalancesnow.png]