Ionospheric irregularities and GPS LoL can affect a wide range of communication and nav igation systems, thus studying and analyzing them using GPS data near the equator and at low latitudes is justified for both scientific and GNSS applications. The purpose of this dis sertation is to investigate nighttime ionospheric irregularity using ROTI and the occurrence characteristics of GPS LoL over Ethiopia , as well as to compare GPS LoL with S4-proxy and S4. In this study, data from the IGS network were used to determine parameters used in this study, including ROTI, S4-proxy, and GPS LoL, however, S4 is derived from the dedicated scintillation receiver of the SCINDA network, and the disturbance storm time index (Dst) is obtained from the World Data Center for Geomagnetism . GPS-TEC software was utilized for processing RINEX observational and navigation files and to create ASCII files that con tain time, azimuth and elevation angles, latitudes, longitudes, and the vertical TEC evaluated along the vertical path above the projections on the Earth of the ionospheric pierce points. Besides to this CRX2RNX from the RTKLIB package was used to convert the RINEX data from CRX (d-extension) format to RNX (o-extension) format. In this work, ROTI is used to represent ionospheric irregularity, and LoL events are found by looking for interruptions in the pseudorange at the GPS-L2 frequency as recorded by the P2 observable in the RINEX files. The results of the nighttime ionospheric irregularity study revealed that values of ROTI larger than 0.5 were recorded in recorded in April, March, and May, while small values of ROTI are observed in the remaining months of the year. In this study, all metrics such as ROTI, S4, S4-proxy, and number of LOL occur more frequently between 21:00 and 23:00 LT. On a monthly basis, on average at the three GPS stations, 75% of the total number of LoL events were recorded in April and March at the GPS receiver locations looked at for this study, whereas the aggregate of the contributions from all remaining months only accounted for 25% of the total. Seasonally, on average, at the three sites, 79.60%, 10.13%, 8.43%, and 1.83% of the total number of LoL occurred during the months of March equinoxes (FMA), September equinoxes (ASO), June solstices (JJM), and December solstices (NDJ), respectively. Annu- ix ally, a total of 551,782 and 160 number of LoL events were detected in Bahir Dar, Debark, and Assosa GPS receiver stations, respectively. LoL events in all stations frequently falls into the region of elevations within 30◦ to 40◦ , and azimuths within 330◦ - 360◦ , and 0◦ -30◦ . LoL events occurred when both S4 and S4-proxy were greater than or equal to 0.7. Low values of S4 and S4-proxy were associated with infrequent LoL occurrence, whereas high values were associated with more LoL occurrences. According to our observations, LoL oc currences and greater S4 and S4-proxy values only happened in the same location of the sky (North-west region) and at the same time. Finally, the results of this study show that ROTI, S4-proxy, and the frequency occurrence of LoL events from IGS network can be utilized to characterize the ionosphere in areas where there is no SCINDA network of GPS receivers. Keywords: GPS LoL, Ionospheric irregularities, Ionospheric scintillation