Sun emits radio energy with a slowly varying intensity. This radio flux, originating from atmospheric layers high in the Sun's chromosphere and low in its corona, changes daily with the sunspot number, and thus also follows the solar cycle. This is seen from the figure displaying the flux at 2800 MHz or 10.7 cm wavelength over the entire solar disk (in here, monthly averages, although daily values exist too). This value is called F10.7, and it is available from continuous routine measurements.
The F10.7 value is used, for example, as an input parameter in models for Earth's atmosphere.