Radiative flux, also known as radiative flux density or radiation flux (or sometimes power flux density), is the amount of
power radiated through a given area, in the form of
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...
s or other elementary particles, typically expressed in watts per square meter (W/m
2). It is used in
astronomy
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...
to determine the
magnitude and
spectral class of a star and in
meteorology
Meteorology is the scientific study of the Earth's atmosphere and short-term atmospheric phenomena (i.e. weather), with a focus on weather forecasting. It has applications in the military, aviation, energy production, transport, agricultur ...
to determine the intensity of the convection in the
planetary boundary layer. Radiative flux also acts as a generalization of
heat flux, which is equal to the radiative flux when restricted to the
infrared spectrum.
When radiative flux is incident on a surface, it is often called
irradiance. Flux emitted from a surface may be called
radiant exitance or
radiant emittance. The ratio of irradiance reflected to the irradiance received by a surface is called
albedo.
Geophysics
Shortwave
In geophysics,
shortwave flux is a result of specular and diffuse reflection of incident shortwave radiation by the underlying surface. This shortwave radiation, as solar radiation, can have a profound impact on certain biophysical processes of vegetation, such as canopy photosynthesis and land surface energy budgets, by being absorbed into the soil and canopies. As it is the main energy source of most weather phenomena, the solar shortwave radiation is used extensively in
numerical weather prediction.
Longwave
Longwave flux is a product of both
downwelling infrared energy as well as emission by the underlying surface. The cooling associated with the divergence of longwave radiation is necessary for creating and sustaining lasting
inversion layers close to the surface during polar night. Longwave radiation flux divergence also plays a role in the formation of fog.
SI radiometry units
See also
*
Spectral flux density
*
Flux
References
{{reflist
Physical quantities
Vector calculus