The Effects of GPS Signal Propagation Paths Alignment with Low-Latitude Ionospheric Field-Aligned Plasma Bubble Structures on Scintillation

This work analyzes GPS scintillation data recorded during five months (Nov/2014 to Mar/2015) at São José dos Campos, Brazil, located near the southern crest of the equatorial ionization anomaly. Analysis has been performed aiming at relating amplitude and phase scintillation indices with the orientation of the propagation path through the ionospheric irregularities and then evaluating its effects on receiver positioning and GPS availability. Based on the analysis of an extensive set with 311,369 samples, it was noted that there is a dominance of intense scintillation events around the azimuth angle of 345º (geographic northwest but nearly aligned with geomagnetic field lines). In view of the large westward magnetic declination (21.4ºW) of this region and of the nature of the plasma bubble irregularity distribution with respect to the geomagnetic field configuration, this result strongly suggests that such GPS signal propagation paths were close to being end-on through magnetic field aligned plasma bubbles. This work will show that during this alignment, the extensive propagation path length through the bubbles can result in larger scintillation intensity cases. Further analysis based on calculation of the propagation angles with respect to the magnetic field line (in elevation and azimuth) clearly support the interpretation that cases of loss of phase lock are most likely to occur for small values of these angles and that those cases are distributed around the value of the scintillation index S4 = 1. Thus, the present work provides for the first time a quantitative verification and confirmation of such effect of scintillation enhancement due to nearly magnetic longitudinal satellite-to-receiver propagation paths. Additionally, this work will show the consequences of such alignment on precise pointing positioning, highlighting the threat that this type of scenario could represent to users of such application.