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Concept information

... > solar system > planet > terrestrial planet > Earth > Earth atmosphere > upper atmosphere > ionosphere > ionospheric D region
... > solar system > atmospheric sciences > Earth atmosphere > upper atmosphere > ionosphere > ionospheric D region

Terme préférentiel

ionospheric D region  

Définition(s)

  • The D layer is the innermost layer, 48 km (30 mi) to 90 km (56 mi) above the surface of the Earth. Ionization here is due to Lyman series-alpha hydrogen radiation at a wavelength of 121.6 nanometre (nm) ionizing nitric oxide (NO). In addition, solar flares can generate hard X-rays (wavelength < 1 nm) that ionize N₂ and O₂. Recombination rates are high in the D layer, so there are many more neutral air molecules than ions. Medium frequency (MF) and lower high frequency (HF) radio waves are significantly attenuated within the D layer, as the passing radio waves cause electrons to move, which then collide with the neutral molecules, giving up their energy. Lower frequencies experience greater absorption because they move the electrons farther, leading to greater chance of collisions. This is the main reason for absorption of HF radio waves, particularly at 10 MHz and below, with progressively less absorption at higher frequencies. This effect peaks around noon and is reduced at night due to a decrease in the D layer's thickness; only a small part remains due to cosmic rays. A common example of the D layer in action is the disappearance of distant AM broadcast band stations in the daytime. (Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/wiki/Ionosphere#D_layer)

Concept(s) générique(s)

Synonyme(s)

  • D region

Traductions

URI

http://data.loterre.fr/ark:/67375/MDL-XBC2DM07-M

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RDF/XML TURTLE JSON-LD Dernière modif. 24/04/2023