Editing Solar cycle (section)

==== Solar radio flux ====
Emission from the Sun at centimetric (radio) wavelength is due primarily to coronal plasma trapped in the magnetic fields overlying active regions.<ref>{{cite journal |author=Tapping K.F. |title=Recent solar radio astronomy at centimeter wavelength: the temporal variability of the 10.7-cm flux |journal=J. Geophys. Res. |volume=92 |issue=D1 |pages=829–838 |date=1987 |doi=10.1029/JD092iD01p00829 |bibcode=1987JGR....92..829T}}</ref> The F10.7 index is a measure of the solar radio flux per unit frequency at a wavelength of 10.7&nbsp;cm, near the peak of the observed solar radio emission. F10.7 is often expressed in SFU or [[solar flux unit]]s (1 SFU = 10<sup>−22</sup> W m<sup>−2</sup> Hz<sup>−1</sup>). It represents a measure of diffuse, nonradiative coronal plasma heating. It is an excellent indicator of overall solar activity levels and correlates well with solar UV emissions.

Sunspot activity has a major effect on long distance [[radio communications]], particularly on the [[shortwave]] bands although medium wave and low [[VHF]] frequencies are also affected. High levels of sunspot activity lead to improved signal propagation on higher frequency bands, although they also increase the levels of solar noise and ionospheric disturbances. These effects are caused by impact of the increased level of solar radiation on the [[ionosphere]].

10.7&nbsp;cm solar flux could interfere with point-to-point terrestrial communications.<ref>{{cite journal |title=The Effect of 10.7 cm Solar Radiation on 2.4 GHz Digital Spread Spectrum Communications |journal=NARTE News |volume=17 |issue=3 |date=July–October 1999 }}</ref>