CHARACTERIZATION OF SPATIO-TEMPORAL VARIATIONS OF POST-SUNSET EQUATORIAL IONOSPHERE

Asfaw, Merid

dc.contributor.author	Asfaw, Merid
dc.date.accessioned	2022-02-11T06:33:44Z
dc.date.available	2022-02-11T06:33:44Z
dc.date.issued	2022-02-11
dc.identifier.uri	http://ir.bdu.edu.et/handle/123456789/13010
dc.description.abstract	Post-sunset ionospheric irregularities are common features of the equatorial ionosphere that affect radio communication and navigation systems. It is known that these irregular ities have shown longitudinal and temporal variations, however, their triggering physical mechanism is not yet fully understood. Also, the characteristics of these irregularities are not well characterized, especially, in the regions where ground ionospheric monitoring facilities have not been deployed with sufficient amount. Therefore, the longitudinal and seasonal variations of equatorial ionospheric irregularities which are also known as Equa torial Plasma Bubbles (EPB) have been characterized and their triggering mechanisms are investigated using ground and space based data. The GPS-data has been used to calculate vTEC depletions, an indicator of EPB, for selected days of both equinox and solstice seasons for the year 2013 at different longitudinal sectors over the equatorial re gion of glob. The results from the GPS vTEC depletion indicated that strong EPB has been observed in the Atlantic and African longitudinal sectors during September equinox and the depletion strength less that -5 TECu has been observed in African sectors in all the season of the year. In addition, the ion density perturbation and plasma vertical drift velocity observations from the C/NOFS satellite and the evening time zonal neutral wind speed observations from the Gravity Field and Steady State Ocean Circulation Explorer (GOCE) satellite are analyzed to investigate the effect of monthly and longitudinal vari ations of the zonal neutral wind speed on the post-sunset vertical-drift velocity and the occurrence rate of EPB. From the analysis results on the effect of zonal neutral wind speed directly on the occurrence of EPB, it is found that at most 21 percent of the longitudinal variations of occurrence of EPB is explained by the longitudinal variations of zonal wind speed only during December 2012. Besides, the longitudinal variations of occurrence of EPB have shown similar pattern with the longitudinal variations of plasma vertical drift velocity. In the Pacific sector, the zonal neutral wind speed, vertical plasma drift velocity, xvi and occurrence of EPB have shown similar longitudinal variations during March equinox. Also, the performance of global horizontal wind model (HWM14) has been investigated using ground FPI data and space based wind speed observations between 80 and 110km from the TIMED Doppler Interferometer (TIDI), and wind speed observations between 220 and 270kms from GOCE satellites. It is found that the performance of the model in describing the TIDI and FPI observations has been similar. To understand the effects of atmospheric waves, characteristics of wavelike oscillation from TEC fluctuation that can be obtained from superposition of different oscillation modes have been investigated. Decomposing fluctuating TEC into different oscillation modes and investigating oscillation characteristics of each component is also important to get insight about the characteristics of individual atmospheric waves that may cause TEC fluctuation. We have investigated characteristics of components of fluctuating TEC obtained from SCINDA GPS receiver installed at Bahir Dar, (geographic coordinate, 11.5 o N, 37.6 oE, and dip latitude of 2.5 oN) Ethiopia during April 2012. First Empirical Mode Decomposition (EMD) has been applied to decompose TEC fluctuation into differ ent oscillation modes that are known as Intrinsic Mode Function (IMF). Hilbert-Huang Transform (HHT) and Continuous Wavelet Transform (CWT) have been applied to inves tigate the characteristics of wave-like oscillations. Applying EMD on fluctuating vTEC corresponding to a GPS satellite. Results from HHT and CWT have shown excellent agreement.	en_US
dc.language.iso	en	en_US
dc.subject	Physics	en_US
dc.title	CHARACTERIZATION OF SPATIO-TEMPORAL VARIATIONS OF POST-SUNSET EQUATORIAL IONOSPHERE	en_US
dc.type	Thesis	en_US