Abstract The focus of this thesis is to determine TIDs characteristics over Ethiopian longitudinal sector using a GPS-TEC data on July, 2013.because of few researchers have been tried to study TIDs characteristics in the Ethiopian longitudinal sector. We are motivated to study the characteristics of TIDs over Ethiopian longitudinal sector by using the ground-based GPS receivers. Calibrated data has been imported into MATLAB code and gave us the result of the value of TEC for each hour, its impact on the GPS(Global Positioning System) signals, both amplitude, and phase, often results in a degraded performance of the GPS receivers. Based on observational data obtained from dual-frequency GPS receivers at two triangular observational networks in three station Bahir dar (11.6 N; 37.35 ◦ E), Seraba (12.061 o N; 37.022 o E) and Debarek (12.021 o E), ionospheric variability of three quiet days on July 2013 is studied using cross-correlation method and TEC measurements. On this day around 17–19.5 LT, a TID was observed from both data sets simultaneously. The TID had a period length of around 2.5 h, and its wave propagated northward with a horizontal phase velocity have been determined in the range of 145–435 m/ s. Keywords.Traveling ionospheric disturbance (TID), Atmospheric gravity wave(AGWs)