Multifrequency spectra of day-time ionospheric amplitude scintillations near the dip equator

Abstract

Power spectra of day-time amplitude scintillations on VHF and UHF signals from the geostationary satellite ATS-6 received at an equatorial station Ootacamund (magnetic dip 6°N) are studied in order to obtain information about long wavelength (≳ 100 m) irregularities generated in the equatorial electrojet plasma. Some of these spectra show Fresnel oscillations, which are usually absent for night-time amplitude power spectra, indicating thereby the presence of a thin layer of irregularities rather than a thick one, as is the case at night. We find that the drift speeds of irregularities estimated from the respective power spectra show expected variations with changes in the electrojet current strength. The high frequency asymptotes of power spectra yield a two-dimensional irregularity power spectrum index of 3.0 ± 0.4 over a wavelength range of approximately 60–800 m, which is close to the value 8/3 predicted by the unified theory of type I and type II irregularities in the equatorial electrojet for the so-called inertial range of wavelengths.