Multi-location study on the scintillation under alignment of GNSS signals with EPB and its effects on positioning in low latitudes

Ionospheric scintillation in the equatorial region significantly degrades Global Navigation Satellite System (GNSS) performance. The geometric alignment between GNSS signal propagation paths and geomagnetic field-aligned plasma bubbles is a critical factor intensifying these effects. However, the spatial heterogeneity of alignment effects and their distinct impacts on various scintillation metrics remain insufficiently explored. This study investigates the influence of signal path alignment with the geomagnetic field on amplitude scintillation, rate of total electron content index (ROTI), and carrier-phase residuals. Over 12 months of scintillation data were collected during the solar maxima of cycles 24 and 25 at four Brazilian stations respectively located near the center and boundary of the Equatorial Ionization Anomaly (EIA). Four alignment cases, namely complete alignment, elevation alignment, azimuth alignment, and non-alignment, are defined. Results reveal that while severe scintillation is generally associated with complete alignment, this dependence is weakened in the EIA center, where high background electron density induces severe scintillation even in non-aligned geometries. Additionally, in contrast to S4, enhanced ROTI values are observed most frequently when the signal paths are nearly orthogonal to the geomagnetic field. Furthermore, Alignment conditions not only intensify measurement errors but also enhance the association between scintillation levels and carrier-phase residuals. Under severe scintillation, alignment conditions can further exacerbate scintillation-related carrier-phase disturbances. These insights contribute to refining scintillation mitigation strategies and optimizing GNSS infrastructure deployment in low-latitude regions.