Signal frequency dependence of ionospheric amplitude scintillations

Abstract

The S₄ index, which is a measure of the strength of amplitude scintillations, is assumed to vary with signal frequency f according to S₄αf^-n, and the frequency exponent n is derived from observed equatorial amplitude scintillations on 40- and 140-MHz signals. A large data base has been used to study the variation of this exponent n(40/140) with the S₄ index on the 140-MHz signal for both daytime and nighttime scintillation events. Although the equatorial E and F region irregularities, which cause the observed scintillation events, have different characteristics, the variation of n(40/140) with S₄(140) is found to be almost universal. Theoretical computation of n(40/140) for different values of the irregularity parameters yields results which are in good agreement with these observations.