F10.7 Solar Radio Measurements.

The following information has been provided by the National Research Council of Canada.

Their data are available by FTP from NOAA at ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SOLAR_RADIO/FLUX

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. Radio intensity levels consist of emission from three sources: from the undisturbed solar surface, from developing active regions, and from short-lived enhancements above the daily level. Solar flux density at 2800 megaHertz has been recorded routinely by radio telescope near Ottawa since February 14, 1947. Each day, levels are determined at local noon (1700 GMT) and then corrected to within a few percent for factors such as antenna gain, atmospheric absorption, bursts in progress, and background sky temperature. Beginning in June 1991, the solar flux density measurement source is Penticton, B.C., Canada.

The tables contain fluxes from the entire solar disk at a frequency of 2800 megaHertz in units of 10 to the -22 Joules/second/square meter/Hertz. Each number has been multiplied by 10 to suppress the decimal point. 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 fluctua- tions as large as 7% that arise from the changing sun-earth distance. In con- trast, adjusted fluxes have this variation removed; the numbers in these tables equal the energy flux received by a detector located at the mean distance be- tween 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.