Auroral E-Region as a Source Region for Ionospheric Scintillation

Altitudinal source regions and generation mechanisms of ionospheric scintillation are investigated by employing the incoherent scatter radar (ISR) at Poker Flat, Alaska (PFISR) and nearby global positioning system (GPS) receivers. Analysis of PFISR and GPS observations during the September 2017 geomagnetic disturbances reveals that phase scintillation is seen during auroral disturbances, and can occur at any storm phase. Statistical comparisons of the rate of change of the total electron content (TEC) index (ROTI) with the amplitude (S-4) and phase (sigma(phi)) scintillation in July-December 2017 show a significant increase with geomagnetic activity and considerable correlations between ROTI and sigma(phi), whereas S-4 showed no noticeable increase or correlations. The PFISR-GPS comparisons show that scintillation occurs when the electron density is enhanced in the auroral E-region and is stronger for larger E-region peak density and/or lower E-region peak altitude. This implies that scintillation is stronger for more intense and/or deeper auroral particle precipitation. A detailed analysis of an event with a well-defined and propagating E-region density enhancement imaged by PFISR reveals that scintillation is stronger on the trailing edge of the density enhancement. This feature is discussed in the context of the gradient-drift instability as a potential mechanism for generation of plasma density waves that scatter GPS radio signals and lead to scintillation. The results of this study add to the growing body of evidence that ROTI can be used as a proxy for phase scintillation and that the ionospheric E-region is an important source region for ionospheric scintillation at auroral latitudes.