Space Weather 101
📻 F10.7 Solar Radio Flux
What is F10.7 Solar Radio Flux?
The F10.7 index measures the intensity of radio emissions from the Sun at a wavelength of 10.7 centimeters, in solar flux units (sfu). Unlike the sunspot number, which relies on visual counting, F10.7 is a direct physical radio measurement — and the two track each other closely, making F10.7 a valuable independent cross-check on overall solar activity.
Why it matters
F10.7 is one of the most consistently measured, longest-running solar activity indices (recorded daily from a ground observatory in Penticton, Canada, since 1947), and it's a key input to models that estimate atmospheric density at satellite altitudes.
Typical values
Quiet-sun (solar minimum) F10.7 typically runs around 65-75 sfu. During solar maximum, it commonly rises to 150-200 sfu or higher, tracking the same 11-year solar cycle as the sunspot number.
How scientists measure it
A radio telescope at the Dominion Radio Astrophysical Observatory in Penticton, British Columbia, measures the Sun's 10.7cm radio emission daily at local noon — a measurement that's remained remarkably consistent for over 75 years.
Why it affects Earth
Higher F10.7 corresponds to more solar ultraviolet and X-ray output, which heats and expands Earth's upper atmosphere, increasing atmospheric drag on low-Earth-orbit satellites — this makes F10.7 a critical input for predicting satellite orbital decay and collision risk.
FAQ
Why 10.7cm specifically?
That wavelength was chosen decades ago because it's easy to measure consistently from the ground, correlates well with overall solar activity, and isn't significantly absorbed by Earth's atmosphere.