The sun emits radio energy with a slowly varying intensity. This radio flux, which originates from atmospheric layers high in the sun's chromosphere and low in its corona, changes gradually from day-to-day in response to the number of spot groups on the disk. Solar flux density at 10,7 cm wavelength has been recorded routinely by radio telescope near Ottawa since February 14, 1947.

Each day, levels are determined at local noon (1700 GMT). Beginning in June 1991, the solar flux density measurement source is Penticton, B.C., Canada. Its observations are available through the DRAO website and all values are also archived at the Space Physics Interactive Data Resource (SPIDR).

Three sets of fluxes - the observed, the adjusted, and the absolute - are summarized. Of the three, the observed numbers are the least refined, since they contain fluctuations as large as 7% that arise from the changing sun-earth distance. In contrast, adjusted fluxes have this variation removed; the numbers in these tables equal the energy flux received by a detector located at the mean distance between sun and earth. Finally, the absolute levels carry the error reduction one step further; here each adjusted value is multiplied by 0,90 to compensate for uncertainties in antenna gain and in waves reflected from the ground.