The solar radio flux at 10.7 cm (2800 MHz) is an excellent indicator of solar activity. Often called the F10.7 index, it is one of the longest running records of solar activity. The F10.7 radio emissions originates high in the chromosphere and low in the corona of the solar atmosphere. The F10.7 correlates well with the sunspot number as well as a number of UltraViolet (UV) and visible solar irradiance records. The F10.7 has been measured consistently since 1947, first at Ottawa, and then at the Penticton Radio Observatory in British Columbia. Unlike many solar indices, the F10.7 radio flux can easily be measured reliably on a day-to-day basis from the Earth’s surface, in all types of weather. Reported in “solar flux units”, (s.f.u.), the F10.7 can vary from below 50 s.f.u., to above 300 s.f.u., over the course of a solar cycle.
The F10.7 Index has proven very valuable in specifying and forecasting space weather. Because it is a long record, it provides climatology of solar activity over six solar cycles. Because it comes from the chromosphere and corona of the sun, it tracks other important emissions that form in the same regions of the solar atmosphere. The Extreme UltraViolet (EUV) emissions that impact the ionosphere and modify the upper atmosphere track well with the F10.7 index. Many Ultra-Violet emissions that affect the stratosphere and ozone also correlate with the F10.7 index. And because this measurement can be made reliably and accurately from the ground in all weather conditions, it is a very robust data set with few gaps or calibration issues.
Atmospheric chemistry and climate