GPS phase and amplitude scintillation at high latitudes during the extreme geomagnetic storm of May 2024

The May 2024 geomagnetic storm was the most intense in recent decades, significantly affecting the Earth magnetosphere and ionosphere. We investigate GPS amplitude and phase scintillation during the main and recovery phases of the storm using GPS receivers including the specialized scintillation receivers of the Canadian High Arctic Ionospheric Network (CHAIN). We primarily compute 30-s scintillation indices using GPS receivers sampling at a 50 Hz rate or higher, complemented by 1-Hz GPS receivers providing a proxy scintillation index. The occurrence of GPS scintillation is studied in the context of ionospheric convection observed by SuperDARN, horizontal equivalent ionospheric currents and estimated vertical current amplitudes derived from the magnetic field measurements by ground magnetometers using the spherical elementary current method, as well as riometer-measured ionospheric absorption, which serves as indicator of energetic particle precipitation. During the main phase of the storm both phase and amplitude scintillation significantly increased following the impact of the interplanetary shock from the coronal mass ejection. The most immediate response was observed at very high latitudes in the cusp region, spreading to auroral and nominally sub-auroral latitudes as the interplanetary magnetic field turned southward. The ionospheric pierce points of strong GPS scintillation were largely collocated with eastward or westward electrojet currents associated with ionospheric convection or mapped near the edges of electrojet regions. In relation to vertical current amplitudes, strong scintillation mapped mostly near the reversal boundaries between downward and upward currents or was collocated with the upward currents. In the recovery phase of the storm, when the geomagnetic disturbances on the nightside were associated with riometer-measured absorption due to auroras, strong phase and moderate amplitude scintillation were observed—particularly when computed for 1-s window to detect short-lived diffractive scintillation.