Abstract:
An important aspect of the development of intermediate-scale length (approximately hundred
meters to few kilometers) 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 postsunset equatorial ionosphere due to
the growth of the Rayleigh-Taylor 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 modeling 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
modeling 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 topside of the equatorial F region than near the equatorial F layer peak.
