LAUSR

An important aspect of the development of intermediate scale length (~100 m – few km) irregularities in an equatorial plasma bubble (EPB) that has not been considered in the schemes to predict the occurrence pattern of L-band scintillations in low latitude regions, is how these structures develop at different heights within an EPB as it rises in the post-sunset equatorial ionosphere due to the growth of the Rayleigh-Taylor (R-T) instability. Irregularities at different heights over the dip equator map to different latitudes, and their spectrum as well as the background electron density determine the strength of L band scintillations at different latitudes. In this paper, VHF and L-band scintillations recorded at different latitudes together with theoretical modelling of the scintillations, are used to study the implications of this structuring of EPBs on the occurrence and strength of L-band scintillations at different latitudes. Theoretical modelling shows that while S4-index for scintillations on a VHF signal recorded at an equatorial station may be > 1, S4-index for scintillations on a VHF signal recorded near the crest of the equatorial ionization anomaly (EIA) generally does not exceed the value of 1 because the intermediate scale irregularity spectrum at F layer peak near the EIA crest is shallower than that found in the equatorial F layer peak. This also explains the latitudinal distribution of L-band scintillations. Thus it is concluded that there is greater structuring of an EPB on the top side of the equatorial F region than near the equatorial F layer peak.