Development of intermediate‐scale structure at different altitudes within an equatorial plasma bubble: Implications for L‐band scintillations. Issue 1 (18th January 2017) - Bhattacharyya, A.
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 S 4 index for scintillations on a VHF signal recorded at an equatorial station may be >1, S 4 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. Key Points: Strong scintillations on VHF signal are recorded near dip equator, while L‐band scintillations are weak Near equatorial ionization anomaly (EIA) crest both VHF and L‐band scintillations may be moderate to strong Model calculations show that equatorial plasma bubble is more structured on the topside of the equatorial F region than near the F peak