A contrasting TEC behaviour over the low-latitude post-midnight sector during recovery phases of May and October 2024 storms: Possible role of PPEF, DDEF, and O/N2

The present study reports on the variability of the post-midnight ionosphere over the low-latitude sector during the recovery phases of the May and October 2024 storms. Multi-instrument observations, comprising GNSS total electron content (TEC), F-layer peak height, and column O/N₂ measurements, were employed to examine this variability. Interestingly, the TEC over the low-latitude American sector showed contrasting behavior on the two nights (11 May 2024 and 11 October 2024). On 11 October 2024, TEC exhibited a significant enhancement exceeding 20 TECu from the post-midnight to morning period, whereas on 11 May 2024, TEC decreased by approximately 5 TECu. The eastward disturbance dynamo electric field (DDEF), driven by storm-time modifications of the thermospheric neutral wind, likely contributed to the significant uplift of the F-layer on 11 October. This uplift also allowed the TEC to remain elevated for a longer period due to reduced quenching at higher altitudes. Additionally, the enhanced O/N₂ also contributed to the elevated TEC on 11 October. Whereas the downward F-layer motion and the associated TEC reduction on 11 May were likely caused by a westward penetration convection electric field (PPEF) during the post-midnight period, with higher quenching at lower altitudes contributing to the observed TEC reduction. The present study evaluates the potential contributions of plasma transport to the contrasting TEC variations and highlighting the distinct roles played by storm time generated electric fields in shaping the dynamics of the low-latitude ionosphere.