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Space Weather

Glossary of Solar Terrestrial Terms

Ultraviolet Radiation

Radiation of immediately shorter wavelengths than visible light, between 5 and 400 nm. Extreme ultraviolet (EUV) and X rays have shorter wavelengths again.

Universal Time

Greenwich Mean Time (GMT). Time referred to the zero meridian of longitude (through Greenwich, UK). 0000 UT is local midnight at Greenwich. For example, 00 UT = 10 am Australian EST = 8 am Australian WST = 9.30 am Australian CST.

Upper Decile

The largest decile, one of nine, that has 90% of the ordered values below it.

Upper Decile MUF

This is a statistical prediction of the highest frequency for HF sky wave propagation. If the prediction is correct, this frequency should be refracted by the ionosphere 10% of the time. See Maximum Usable Frequency and Optimum Working Frequency.

UT

See Universal Time.

UV

See Ultraviolet Radiation.

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