Effective Index of Solar Activity for Long-Term Forecast of the Ionosphere

From analysis of the ionospheric (T) and solar (Ri and F) indices of solar activity, an effective solar index F* was derived which is calculated using F - the flux of solar radiation at the wavelength of 10.7 cm. All these indices are the sliding average indices over 12 months which are centered to the middle of a specific month. The index F* proved to be more exact than the indices derived from the international sunspot numbers (Ri or Rz) for the solar cycle 24. Therefore the index F* can be recommended instead of the index Rz in calculations of foF2 medians in the IRI model.