Study of equatorial ionospheric irregularities using space tethered, multipoint technique and coordinated ground-based FPI and scintillation measurements.

Abstract

Technological advances are exploiting the Earth's ionosphere for the purpose of communication and navigation spurring a need to understand the ionospheric irregularities which can have adverse effects on these signals. This dissertation studies equatorial spread F (ESF) irregularities using two different measurement techniques, namely, space-based simultaneous, multi-point measurements and ground-based Fabry-Perot Interferometric (FPI) and scintillation measurements. The TSS-1R mission (1996) provided a novel technique for probing the ionosphere using multiple space tethered sensors to simultaneously sample the ionosphere in the horizontal and vertical scales. Studies using data from this mission indicate that ESF irregularities can have very complex structures with sharp gradients and structuring over vertical scale lengths of the order of 10 km, at 300 km altitude. Large eastward tilt of 55&deg; over this altitudinal scale was observed. Thus, the study has not only provided the first ever simultaneous, <italic> in situ</italic>, multi-point measurements of ESF morphology, but has also demonstrated the feasibility and potential of using space tethered sensors, flying in formation, to explore irregularities in a two dimensional space scale. Low-latitude, coordinated studies using FPI neutral wind data and ionospheric scintillation measurements from Chile between July--October, 1997, examined the extent of plasma-neutral coupling in the nighttime ionosphere. A correlation between zonal wind characteristics and the occurrence/intensity of spread F was observed. A modest dependence was seen between the meridional winds and spread F. A very high degree of coupling existed between the monthly-averaged zonal winds and irregularity drifts, especially after 2100 LT, suggesting that the F region polarization electric fields are well developed. This provided experimental confirmation of the role of the F region dynamo as the primary driver of the nighttime electrodynamics. Comparison of this study with data from two near-magnetic equatorial sites in Peru showed the existence of latitudinal coherence in plasma-neutral coupling. Thus, the localized winds can exert a strong control over the field-aligned irregularity drifts over at least 7&deg;. The wind and scintillation drift velocities were seen to be higher in Peru, as expected. Simple modeling studies for the Chilean site have been performed for comparison with the experimental results.