How Ionospheric Scintillation Disrupts GNSS Accuracy After Sunset Near the Equator

Ionospheric scintillation is a phenomenon where irregular fluctuations in electron density distort GNSS signal phase and amplitude, causing positioning accuracy to degrade significantly. It occurs most intensely near the geomagnetic equator — affecting regions such as Brazil, Nigeria, India, and Singapore — and is triggered daily by sunset, with disruptions lasting several hours into the night. The severity is measured by two indices, S4 for amplitude and sigma-phi for phase, with strong scintillation defined at S4 above 0.6 and sigma-phi above 0.3. Effects on receivers range from metre-level position drift in mild cases to complete loss of signal lock in extreme events, with RTK systems particularly vulnerable to cycle slips. Since the corruption originates in the signal itself rather than satellite geometry, simply adding more constellations does not resolve the issue, requiring instead specialised receiver technology designed to handle scintillation conditions.