Editing Solar cycle (section)

==== Short-wavelength radiation ====
[[File:The Solar Cycle XRay hi.jpg|thumb|left|upright=1.35|A solar cycle: a montage of ten years' worth of [[Yohkoh]] SXT images, demonstrating the variation in solar activity during a solar cycle, from after August 30, 1991, to September 6, 2001. Credit: the Yohkoh mission of [[Institute of Space and Astronautical Science|ISAS]] (Japan) and [[NASA]] (US).]]
With a temperature of 5870 K, the [[photosphere]] emits a proportion of radiation in the [[extreme ultraviolet]] (EUV) and above. However, hotter upper layers of the Sun's atmosphere ([[chromosphere]] and [[solar corona|corona]]) emit more short-wavelength radiation. Since the upper atmosphere is not homogeneous and contains significant magnetic structure, the solar ultraviolet (UV), [[Extreme ultraviolet|EUV]] and X-ray flux varies markedly over the cycle.

The photo montage to the left illustrates this variation for soft [[X-ray]], as observed by the Japanese satellite [[Yohkoh]] from after August 30, 1991, at the peak of cycle 22, to September 6, 2001, at the peak of cycle 23. Similar cycle-related variations are observed in the flux of solar UV or EUV radiation, as observed, for example, by the [[Solar and Heliospheric Observatory|SOHO]] or [[TRACE]] satellites.

Even though it only accounts for a minuscule fraction of total solar radiation, the impact of solar UV, EUV and X-ray radiation on the Earth's upper atmosphere is profound. Solar UV flux is a major driver of [[Stratosphere|stratospheric chemistry]], and increases in ionizing radiation significantly affect [[ionosphere]]-influenced temperature and [[electrical conductivity]].
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