Insolation (from the Latin insolare “expose to the sun”, “warm”), also solar radiation , is the incidence of solar radiation on a surface or a body. In the geosciences , the insolation is the flow of solar radiation falling on part of the earth's surface , the sea surface or the atmosphere , in ecology the flow of solar radiation falling into an ecosystem, in medicine a synonym for sunstroke . Insolation as a physical quantity is a radiation flux density with the unitWatts per square meter (W / m 2 ). The radiation flux density per wavelength is the irradiation , in W / (m 2 · μm).
Insolation above the earth's atmosphere is described by the solar constant . Part of the solar radiation is reflected in the earth's atmosphere, part is absorbed and scattered (→ extinction ). If one looks at the insolation on the earth's surface, there is also the indirect, diffuse sky radiation in addition to the direct sunlight that casts shadows ; the sum of direct and diffuse radiation is called global radiation . It is measured with a pyranometer . The direct radiation at a location can be measured with pyrheliometers or actinometers . The insolation at a place on earth depends on the angle of incidence of the sun and thus on the geographical latitude , the exposure of the area , time of day and season (→ Lambert's law ). Cloudiness in the atmosphere can reduce the insolation of the earth's surface.
Almost all of the energy that is effective on the surface and in the atmosphere in the climate system reaches the earth through solar radiation . It also has an effect on the soil and rocks and causes noticeable fluctuations in the soil temperature when the irradiation changes , which contribute to mechanical weathering (→ insolation weathering ). These phenomena include core cracks and flaking . Furthermore, the insolation causes meteorological phenomena such as the steady onshore wind on elongated coasts : During the day, the land warms up faster than the sea due to the insolation, which means that air over the land tends to rise and flow in from the sea.
The orbit of the earth around the sun as well as the precession and the inclination of the earth's axis fluctuate cyclically over a period of tens of thousands to hundreds of thousands of years. As a result, the angles of incidence and the distribution of solar radiation change in the northern and southern hemisphere. These insolation fluctuations partly explain, in connection with feedback effects, natural climate changes on earth, including the change between the cold and interglacial periods of the Cenozoic Ice Age (→ Milanković cycles ). The radiation emanating from the sun is also subject to changes and fluctuations on different time scales, which are reflected in changes in the solar constants. According to the standard model of the sun, its radiant power increases gradually, by about a third over the course of the earth's 4.5 billion years . In addition, a number of activity cycles are suggested, spanning thousands to hundreds of years. The approximately 11-year Schwabe cycle , which is associated with a slight change in the solar constant of around 1 W / m 2 , has been reliably proven .
The energy of the sun is e.g. B. via photosynthesis , of crucial importance for living things . In medicine, the insolation on the human organism and its duration - solar radiation - is considered. Excessive exposure to the sun on the head can one even Insolatio , insolation or Insolationsenzephalitis called sunstroke cause. In dermatology, the sun exposure of human skin is considered as it occurs when sunbathing .
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- Alan H. Strahler, Arthur N. Strahler: Physical geography . UTB, 2009, ISBN 978-3-8252-8159-5 , section "Insolation", p. 73-76, 107 .
- Insolation. In: Spectrum Lexicon of Geosciences. Retrieved April 17, 2020 .
- Matthias Schaefer: Dictionary of Ecology . Springer, 2012, p. 72 , keyword “radiation” .
- Irradiation. In: Spectrum Lexicon of Geosciences. Retrieved April 20, 2020 .
- Jürgen Schultz: The ecological zones of the earth . UTB, 2016, ISBN 978-3-8252-4628-0 , chapter "2.1 Radiation climate", p. 29-31 .
- Wilhelm Kuttler: General climatology (= general geography floor plan ). UTB, 2009, ISBN 978-3-8252-3099-9 , chapter "4.3 Reception of radiation on earth", p. 62-63 .
- Insolation fluctuations. In: Spectrum Lexicon of Physics. Retrieved April 20, 2020 .
- Dagmar Reiche (Ed.): Roche Lexicon Medicine . 5th edition. Elsevier, 2003, ISBN 978-3-437-15156-9 , keywords “Insolatio. Insolation ”and“ Insolation encephalitis ” .