Browsing by Author "Geoffrey, Cele"

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    Assessment of the Performance of International Reference Ionosphere Models 2016 and 2020 in Predicting TEC in the Low-Latitude Ionosphere over Africa and South America
    (Elsevier, 2025-10-15) Geoffrey, Cele; Geoffrey Andima; Valence Habyarimana; Edward Jurua; Oyirwoth Patrick Abedigamba
    The sparse distribution of Global Navigation Satellite System (GNSS) receivers in low-latitude region has hindered continuous monitoring of the ionosphere. To address this challenge, ionospheric models such as the International Reference Ionosphere (IRI) are often used. This study compares the performance of IRI-2020 and its predecessor (IRI-2016) with the Global Positioning System (GPS) observations over African and South American low-latitude regions during quiet conditions. The GPS Vertical Total Electron Content (VTEC) measurements from Addis Ababa (Geog. 38.77°E, 9.04°N), Sao Luis (Geog. −44.21°E, −2.59°N), Malindi (Geog. 40.19°E, −3.00°N), Libreville (Geog. 9.67°E, 0.35°N), Brasilia (Geog. −47.88°E, −15.95°N) and Cacoheira Paulista (Geog. −45.00°E, −22.68°N) stations for the high, moderate and low solar activity years 2014, 2016 and 2018 were compared with IRI-derived VTEC values. To objectively assess the model accuracy, the Mean Absolute Percentage Error (MAPE) and Normalized Root Mean Squared Error (NRMSE) metrics were employed, offering intuitive and reliable benchmarks for quantifying the model discrepancies. The monthly performance indicates that IRI-2020 and its predecessor significantly underestimate VTEC over Addis Ababa, yet slightly overestimate it over Libreville and Cacoheira Paulista across all studied years. Seasonal analysis reveals the largest discrepancies at the Equatorial Ionisation Anomaly (EIA) trough and Southern crest during solstice seasons. An evaluation of the latitudinal performance of IRI-2016 and IRI-2020 highlights better accuracy over the EIA trough. Furthermore, longitudinal assessment shows superior performance of both models at Libreville station, with IRI-2020 and IRI-2016 achieving notably low annual MAPE (aMAPE) values of and , respectively. Comparative analysis based on NRMSE shows IRI-2020’s improvement of at the dip equator, while its performance declines by at the EIA Southern crest. This study reveals significant discrepancies in the performance of IRI-2020 model over Africa and South America low-latitude, emphasizing the need for continuous model improvement.