STATISTICAL STUDIES OF AN EFFECTIVE SUNSPOT NUMBER

Two decades ago, the U.S. Air Force Air Weather Service space forecast ing group began generating what was termed an effective sunspot number (SSNe) by fitting a model of the critical frequency of the F-2 layer (f(0)F(2)) to observed f(0)F(2) values. Initially a preprocessing step in a larger analysis package, this parameter has taken on a life of i ts own and is now used in various applications for both forecasts and specification of the global f(0)F(2) field. This paper describes the v arious ways in which this parameter is calculated, investigates the be havior of this parameter over solar cycle 21 (1976 through 1986), and compares it with other solar-ionospheric indices, including R-12, IF2, IG, and the Ionospheric Prediction Service (IFS) T index.