On the Effect of “Patchy” Aurora and Auroral Arcs on GPS Signals: Initial Investigations

Abstract:

Aurora occurs in different well-known morphologies, or types, including the best-known arcs and patchy-pulsating aurora (PPA). Previous observational studies have demonstrated that the ionospheric effects of auroral precipitation affect the accuracy of global navigation satellite systems, but how different types of aurora might affect GNSS differently has not been investigated to date. In an initial attempt to explore the relationship between auroral type and the resulting effects on GNSS, we have used data from a THEMIS (Time History of Events and Macroscale Interactions during Substorms) All-Sky Imager (ASI) located at Sanikiluaq (~67º geo.mag. lat.), Canada. GPS data was also obtained from a Canadian High Arctic Ionospheric Network (CHAIN) GPS receiver collocated with the THEMIS ASI. This GPS receiver is a commercial GPS scintillation receiver. A list of 140 patchy aurora events and 180 auroral arc events were catalogued from the ASI data for the years 2008-2013. Corresponding scintillation data for these time periods were obtained from the GPS receiver. In order to determine the effects of PPA and arcs on GPS signals, the number of cycle slips observed during each event were calculated. A total number of 197 cycle slips were observed during PPA compared to 16 cycle slips observed during arcs. This result suggests PPA affects GPS in a more adverse manner than auroral arcs. Even though the magnitude of the phase scintillation index (σ_φ) observed for auroral arcs was much higher than for PPA, the receiver was able to keep lock on to the signals much better during arcs compared to patchy aurora. We have also calculated spectral slopes/spectral index for all events which had σ_φ > 0.3. We obtained around 1500 spectral slopes for events during auroral arcs and around 600 for events during patchy aurora. Although the histograms for these spectral indices seem to reveal that average spectral index for both of these phenomena was ~3.5, spectral indices for auroral arcs seem to tend towards higher values compared to spectral indices of PPA. This result seems to suggest that for auroral arcs, large sized ionospheric irregularities dominate their spectral content compared to PPA. Elevation-angle and azimuthal distributions of PPA and arcs were also considered in this study.