## 4 Discussion
MSTIDs are typically observed minutes before the onset of SF, with perturbations intensifying and breaking into small-scale structures that eventually drift towards the topside region. [PERSON] et al. 2018 [19] provided evidence of instabilities with significant plasma density upwelling, extending well into the topside. Numerical midlatitude ionosphere simulationscapture key features, including patchy Es layers, MSTIDs, bottomside spread F, and topside irregularities. These simulations emphasize the pivotal role of intense GWs propagating into the thermosphere, driving ionospheric dynamics. GW-induced wind fields form and structure Es layers, trigger MSTIDs through dynamo effects, and drive F-region currents that produce bottomside irregularities. GW-induced electric fields in the E-region are mapped along magnetic field lines into the topside, generating irregularities through convection and advection [19]. The present study analyzed the association between enhanced ROTI and Swarm Ne fluctuations during SF activity. Out of ten cases, six (Cases 1, 4, 5, 8, 9, and 10) exhibited this association. Consistent with [PERSON] et al. 2016 [34], the results confirm a robust relationship between ROTI and concurrent in situ Ne data from Swarm, with seasonal and longitudinal patterns aligning for topside ionospheric irregularities. In the present study, a high ROTI value was defined as ROTI \(>\) 0.15 TECU/min, [23]. In all six cases, hmF2 exceeded 350 km, suggesting that SF activity, under favourable conditions, facilitates the uplift of small-scale irregularity structures. These irregularities drift to the topside ionosphere, impacting Swarm Ne and contributing to the formation of topside irregularities, as evidenced by high ROTI values in the L-band. According to [PERSON] et al. 2019 [45], ST and MREs indicate weak TID activity on ionograms. In this study, one MRE event (Case 2) and two ST events (Cases 8 and 9) were recorded, but none were associated with fluctuations in the Swarm Ne latitude profile. This finding appears contradictory, given that MSTIDs are known triggers for SF formation and their strong association with SF-linked topside irregularities has been established. However, this can be explained by the transient nature of ST and MRE traces. Previous studies [18; 45] have noted that these structures typically persist for only 5-10 min before disappearing, and they may reappear intermittently. Therefore, while ST and MREs represent irregularity wavefronts similar to TIDs, their short-lived manifestation and limited impact likely make their influence insufficient to generate significant fluctuations in the Swarm Ne latitude profile. An interesting observation arises from Cases 6 and 7, where Swarm A-C Ne latitude profiles between 02:20 and 03:30 UT, across 53-67\({}^{\circ}\) N latitude and \(-\)5\({}^{\circ}\) to 2\({}^{\circ}\) E longitude, showed a clear density depletion, with Ne at 2 \(\times\) 10\({}^{4}\) elect/cc. However, Swarm B Ne profiles over the same region recorded no such depletions. Unfortunately, the lack of data from ground- or space-based instruments in this region, located over the Atlantic Ocean, prevents further investigation. Despite this limitation, high hmF2 values recorded at the nearest Digisonde station, Fairford, provide some context. In Case 6, Fairford recorded hmF2 at 352 km, while in Case 7, it was 382 km, indicating a significant F-layer uplift. This uplift likely exceeded the orbital altitude of Swarm A-C but remained near the altitude of Swarm B, explaining the discrepancy in Ne observations. Similar findings were reported by [PERSON] et al. 2022 [43], who concluded that midlatitude irregularities are more prevalent at Swarm B altitudes, further supporting this interpretation. Case 10 is the only example of SF-associated topside ionospheric irregularity observation under the influence of a geomagnetic storm.