Browsing by Author "Yemane, Tesfay"

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    Radiowave Scintillation over Ethiopia using Scinda GPS Stations
    (Addis Ababa University, 2007-09) Yemane, Tesfay; Mengistu, Gizaw (Professor)
    The low latitude and equatorial ionosphere TEC and S4 index variability are investigated using observational data. Two GPS stations namely Addis Ababa located at geographic latitude 9°.034 N and longitude 38°.67 E and Bahrdar station geographic latitude 11°.37 N and longitude 37°.10 E are analyzed for the ascending period of solar cycle 24. During the period of observation (January 2008 to December 2014), the variation of scintillations with diurnal, seasonal, magnetic activity, low and high solar activity are presented in this thesis. Due to geographical location in uence there were a time shift of peak VTEC and S4 at both Addis Ababa and Bahir Dar. The occurrence of scintillation is found to be hourly mean maximum in E-season and minimum in D-season. The suppression or enhancement of pre-midnight scintillations during magnetic disturbed and quiet periods is found to be a local time dependent. When the occurrence of geomagnetic storm was observed either to inhibit or to trigger scintillation occurence. Enhanced scintillation appeared during main and recovery phase of geomagnetic storm. Scintillation was maximum during high sunspot number (2011-2014) and was minimum at low sunspot number (2008-2010). Post-sunset scintillation was found to be maximum in E-season whereas it is minimum in D-season. The elevation angle of PRN satellites have an in uence on scintillation occurence. Pre- reversal enhancement of VTEC is a cause to maximum scintillation ascending during post-sunset. Keywords: GPS-SCINDA; VTEC, S4 index, Dst, elevation angle, Geomagnetic storm, low solar activity period, high solar activity period
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    Radiowave Scintillation over Ethiopia using Scinda GPS Stations
    (Addis Ababa University, 2015-07) Yemane, Tesfay; Mengistu, Gizaw (Professor)
    The low latitude and equatorial ionosphere TEC and S4 index variability are investigated using observational data. Two GPS stations namely Addis Ababa located at geographic latitude 9°.034 N and longitude 38°.67 E and Bahrdar station geographic latitude 11°.37 N and longitude 37°.10 E are analyzed for the ascending period of solar cycle 24. During the period of observation (January 2008 to December 2014), the variation of scintillations with diurnal, seasonal, magnetic activity, low and high solar activity are presented in this thesis. Due to geographical location in uence there were a time shift of peak VTEC and S4 at both Addis Ababa and Bahir Dar. The occurrence of scintillation is found to be hourly mean maximum in E-season and minimum in D-season. The suppression or enhancement of pre-midnight scintillations during magnetic disturbed and quiet periods is found to be a local time dependent. When the occurrence of geomagnetic storm was observed either to inhibit or to trigger scintillation occurence. Enhanced scintillation appeared during main and recovery phase of geomagnetic storm. Scintillation was maximum during high sunspot number (2011-2014) and was minimum at low sunspot number (2008-2010). Post-sunset scintillation was found to be maximum in E-season whereas it is minimum in D-season. The elevation angle of PRN satellites have an in uence on scintillation occurence. Pre- reversal enhancement of VTEC is a cause to maximum scintillation ascending during post-sunset Keywords: GPS-SCINDA; VTEC, S4 index, Dst, elevation angle, Geomagnetic storm, low solar activity period, high solar activity period.