Jump to content

Solar variation

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by SEWilco (talk | contribs) at 02:37, 19 June 2004 (→‎Solar cycles: Faculae -> faculae). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Solar variation refers to fluctuation in the amount of energy emitted by the Sun. The Sun is a star undergoing hydrogen to helium fusion reactions due to compression deep inside. The rate of reactions is sufficiently constant that the amount of solar radiation emitted at the surface does not change much. Small variations have been measured from satellites during recent decades.

Sunspots

Sunspots are relatively dark areas on the surface of the Sun. They have been determined to be cooler than its average surface. Variations in their numbers alter the brightness of parts of the Sun.

Solar cycles

Solar cycles are cyclic changes in behavior of the Sun. Most obvious is a gradual increase and decrease of the number of sunspots over a period of about 11 years, called the Schwabe cycle. This seems to be due to a shedding of entangled magnetic fields. The Sun's surface is also the most active when there are more sunspots, although the luminosity does not change much due to an increase in bright spots (faculae). Other patterns detected are the Hale cycle (22 years) and the Gleissberg cycle (70-100 years).

Solar luminosity

The overall brighness of the Sun has been found to vary slightly during a few recent solar cycles. It has been most directly measured by satellites above the atmosphere. Comparisons between ground instruments, high-altitude instruments, and instruments in orbit have been used to calibrate ground instruments. Researchers have combined present readings and factors to adjust historical data. Also used have been proxy data, such as measurements of cosmic ray isotopes to infer solar magnetic activity and thus the likely brightness.

Solar irradiance

Solar irradiance is the amount of sunlight which reaches the Earth. The equipment used might measure optical brightness, total radiation, or radiation in various frequencies. Historical estimates use various measurements and proxies.

There are two types of measurements used:

  • the amount reaching the upper atmosphere
  • the amount reaching some point within the atmosphere, including the surface.

Climate models are computer simulations which are used to examine understanding of climate behavior. Some models use constant values for solar irradiance, while some include the effects of a variable Sun.

Global warming

Many researchers have correlated solar variation with changes in the Earth's average temperature and climate. The effects have always exceeded the amount of solar change, so changes are amplified by the Earth's atmosphere. There is dispute whether current global warming is primarily due to solar variation or due to changes in the atmosphere.

The global warming solar variation theory claims that irradiation changes are having greater effects than atmospheric changes.

This has become a political issue to proponents of the anthropogenic global warming theory, which claims that artificial increases in carbon dioxide in the atmosphere have a greater effect than solar radiation, and who have demanded controls on emissions. Control of solar irradiation has not received much attention.

See Global warming for further information on warming effects and climate change for information on other factors in climate change.


Retrieved from "https://en.wikipedia.org/w/index.php?title=Solar_variation&oldid=4164890"