Atmospheric Radiation and Energy Balance
How solar and terrestrial radiation propagate through, are absorbed and emitted by, and are scattered within the atmosphere, setting Earth's planetary energy balance.
Definition
Atmospheric radiation and energy balance is the study of electromagnetic radiation in the atmosphere and of the resulting flows of energy that determine the temperature structure of the Earth-atmosphere system.
Scope
This area covers the transfer of shortwave (solar) and longwave (terrestrial) radiation through the atmosphere, the absorption and emission of radiation by gases, clouds and aerosols, the partitioning of incoming solar energy among reflection, absorption and surface heating, and the longwave trapping that produces the greenhouse effect. It links the microphysics of molecular and particle interactions with radiation to the macroscopic top-of-atmosphere energy budget that drives climate.
Sub-topics
Core questions
- How is solar radiation absorbed, scattered and reflected as it passes through the atmosphere?
- What controls the emission of longwave radiation to space and back toward the surface?
- Why is Earth's surface warmer than its radiative equilibrium temperature would predict?
- How do small changes in atmospheric composition perturb the planetary energy balance?
Key theories
- Radiative transfer theory
- A formal description, via the radiative transfer equation, of how radiant intensity changes along a path through an absorbing, emitting and scattering medium; the basis for all quantitative atmospheric radiation calculations.
- Planetary energy balance
- The principle that, at equilibrium, absorbed solar radiation equals outgoing longwave radiation, so the top-of-atmosphere net flux constrains global mean temperature.
Mechanisms
Incoming solar radiation peaks in the visible; about 30% is reflected (planetary albedo) and the remainder is absorbed by the surface and atmosphere. The warmed surface and atmosphere emit longwave radiation following Planck's law modified by emissivity; greenhouse gases absorb and re-emit this longwave radiation, reducing the net loss to space and raising surface temperature. The balance is described by the radiative transfer equation combining Beer-Lambert absorption with thermal emission and scattering source terms.
Clinical relevance
Quantifying radiative fluxes underpins climate modeling, remote sensing retrievals of temperature and composition, solar energy resource assessment, and the definition of radiative forcing used in climate-policy assessments.
History
The radiative basis of atmospheric warming was outlined by Joseph Fourier and quantified by John Tyndall's measurements of gas absorption and Svante Arrhenius's 1896 carbon-dioxide calculation. Chandrasekhar formalized radiative transfer theory in the mid-twentieth century, and satellite-era measurements since the 1980s have constrained Earth's energy budget to within a few watts per square metre.
Key figures
- Svante Arrhenius
- Subrahmanyan Chandrasekhar
- Kevin Trenberth
Related topics
Seminal works
- trenberth2009
- liou2002
- wallaceHobbs2006
Frequently asked questions
- What is the difference between shortwave and longwave radiation?
- Shortwave radiation is the solar energy received by Earth, concentrated in visible and near-infrared wavelengths; longwave radiation is the thermal infrared emitted by the cooler Earth and atmosphere. The atmosphere is largely transparent to shortwave but strongly absorbs longwave.
- Why is Earth warmer than a simple radiation balance predicts?
- Greenhouse gases absorb outgoing longwave radiation and re-emit part of it back toward the surface, so the surface must be warmer than the planet's effective radiating temperature to balance the energy budget.