Ionospheric Indices: IF2 AND IG
The IF2 and IG indices of solar activity are derived from the monthly median noon foF2 data available from the following thirteen ionospheric observatories:
The IF2 index values given in the Ionosperic Indices table continue the series of tabulated values issued on 25 March 1982 for the period 1938-1980.
The IG index has been confirmed as an alternative to sunspot number when predictions of foF2 are being prepared with the aid of the CCIR atlas of ionospheric characteristics. The values given in the Ionospheric Indices table continue the series of tabulated data for the period 1943-1980 published in the ITU Telecommunication Journal (Vol 50, Aug 1983, p 408) where the index was referred to as the Global Effective Sunspot Number(GESSN).
When foF2 data are late in arriving, provisional index values are calculated and are shown in parentheses; the final values will be published later. It should be pointed out that the Ionospheric Index does not contain predicted values of the indices; these are published each month, for periods up to six months ahead, in the ITU Telecommunications Journal.