Significant Enhancement of Nighttime Mid‐Latitude Ionospheric Periodic Perturbations Associated With MSTIDs During the 2020/2021 SSW

Abstract

Utilizing GNSS, ionosonde, meteor radar, and multiple satellite observations, this study investigates the enhancement of nighttime mid‐latitude ionospheric periodic perturbations associated with medium‐scale traveling ionospheric disturbances (MSTIDs) over China sector during the 2020/2021 major sudden stratospheric warming (SSW). GNSS measurements reveal a sustained increase in nighttime TEC perturbations, characterized by mesoscale structures with predominantly southwestward propagation. Concurrent plasma‐density fluctuations observed by Swarm and CSES‐1, together with enhanced spread F in ionosonde measurements, show that the enhanced variability was detected by multiple independent instruments. The perturbation enhancement was accompanied by intensified sporadic‐E (Es) activity. Meteor‐radar observations, JAWARA reanalysis, and ICON HME results further show enhanced semidiurnal tidal activity, particularly SW2, together with increased vertical ion convergence near the observed Es‐layer heights. These concurrent changes support SSW‐related lower‐atmospheric preconditioning, while the correspondence between enhanced Es activity and F‐region perturbations is consistent with possible Es–F‐region electrodynamic coupling. Geomagnetic forcing also likely contributed: the largest daily perturbation enhancement occurred near the weak geomagnetic storm on 12 January, whereas elevated activity persisted during several comparatively quiet intervals. Regional gravity‐wave activity did not show a sustained enhancement sufficient to explain the persistent ionospheric response. Overall, the observations suggest contributions from both SSW‐related lower‐atmospheric variability and episodic geomagnetic forcing, whereas their relative roles and possible coupling remain unresolved.