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10.7cm Solar Radio Flux
(Observed and Derived from GPS IONO Model)


Note: Heavy (dark) lines are for the current 27-day Bartel rotation; light lines are for the last rotation.

The F10.7 index is a measure of the noise level generated by the sun at a wavelength of 10.7 cm at the earth's orbit. The global daily value of this index is measured at local noon at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, Canada. Historically, this index has been used as an input to ionospheric models as a surrogate for the solar output in wavelengths that produce photoionization in the earth's ionosphere (in the ultraviolet bands). The heavy dashed line indicates the maximum observed 10.7cm flux for this solar cycle.

The GPS-derived F10.7 index is inferred from the ionospheric model coefficients transmitted in the GPS navigation signal. This model, developed specifically for GPS single-frequency users by J. Klobuchar, provides estimates of the effect of the ionosphere on the GPS frequencies as a function of location on the earth, time-of-day, season, and the 10.7cm solar radio flux (F10.7). This index is generated daily at NWRA from the latest values of the GPS ionosphere coefficients obtained from the NOAA NGS CORS site. The A0 coefficient from the full set is used to infer the F10.7 used to generate the coefficients in the GPS message via interpolation in a table of A0 as a function of day-of-year and F10.7.

Further information about the GPS ionosphere model and how the coefficients are generated can be found in the following references:

  • Klobuchar, J.A., Ionospheric time-delay algorithm for single-frequency GPS users, IEEE Trans. Aerospace and Electronic Sys., AES-23, 325-331, 1987.
  • Feess, W.A. and S.G. Stephens, Evaluation of GPS ionospheric time-delay model, IEEE Trans. Aerospace and Electronics Sys., AES-23, 332-338, 1987.

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