Ionospheric scintillation during the recovery phase of the May 2024 superstorm over mid- and low-latitude East Asia

Observations of strong GNSS scintillation over low- and middle-latitude East Asia during geomagnetic storm recovery phases remain limited, especially those combining multiple GNSS stations, multiple constellations, and ionosonde measurements. This study used GPS, BDS, and Galileo observations from five GNSS stations of the Chinese Meridian Project, together with measurements from three colocated digital ionosondes, to investigate the spatial and temporal evolution of ionospheric scintillation and related F-region structures during the recovery phase of the May 2024 super geomagnetic storm over the low- and middle-latitude region of East Asia. The results showed that strong amplitude scintillation mainly occurred from 20:00 to 23:00 UT on 11 May 2024, corresponding to the predawn period over East Asia. This occurrence was clearly different from the weaker scintillation observed during the storm main phase and the same UT interval on the following day. Significant S 4 enhancements were observed in multiple GNSS constellations, and peak values exceeded 1.0 on some satellite links. Stations at different longitudes showed a clear time delay, with earlier scintillation enhancement in the east and later enhancement in the west. Using scintillation-enhancement onset-time differences and the corresponding zonal IPP separations, we estimated an apparent westward progression speed of approximately 135 m/s. TEC variations from BeiDou GEO satellites with nearly fixed IPPs, regional TEC maps, and ROTI distributions further showed that TEC enhancements, local depletion structures, and ROTI-active regions during the recovery phase had a consistent westward evolution pattern. Spread-F activity observed by digital ionosondes showed good temporal agreement with the GNSS scintillation enhancements. These observations provided independent evidence for complex F-region structures and irregularity activity during the recovery phase. These results provide new observational constraints for understanding the mechanisms responsible for anomalous ionospheric scintillation and its relationship with spread-F phenomena under extreme space weather conditions in the low- and middle-latitude region of East Asia.