  In this paper we study how GPS, GLONASS, and Galileo navigation signals are
compromised by strong irregularities causing severe phase scintillation
($\mathit{\sigma }_{\phi }$ > 1) in the nightside high-latitude ionosphere
during a substorm on 3 November 2013. Substorm onset and a later
intensification coincided with polar cap patches entering the auroral oval to
become auroral blobs. Using Global Navigation Satellite Systems (GNSS)
receivers and optical data, we show severe scintillation driven by intense
auroral emissions in the line of sight between the receiver and the satellites.
During substorm expansion, the area of scintillation followed the intense
poleward edge of the auroral oval. The intense auroral emissions were colocated
with polar cap patches (blobs). The patches did not contain strong
irregularities, neither before entering the auroral oval nor after the aurora
had faded. Signals from all three GNSS constellations were similarly affected
by the irregularities. Furthermore, two receivers spaced around 120km apart
reported highly different scintillation impacts, with strong scintillation on
half of the satellites in one receiver and no scintillation in the other. This
shows that areas of severe irregularities in the nightside ionosphere can be
highly localized. Amplitude scintillations were low throughout the entire
interval.
