## 4 Discussion
Regarding the vertical plasma redistribution, three uplift phases can be distinguished (Figure 4):  
(1) 18:30-19:30 UT (SO) and 18:37-19:37 UT (VT): Simultaneous parallel variations with similar speeds (around 31 m/s at SO and 52 m/s at VT), likely driven by the same global electric fields, initially PPEF, later with contribution from DDEF. The study of [PERSON] et al. [74] strengthens this scenario, while they observed signatures of strong unshielded PPEF (between 17:05 UT, and until \(\sim\)19:40 UT). This caused an increase of the equatorial ExB drifts up to 95 m/s, which led to the occurrence of a strong ionospheric super-fountain effect around the equator. Most probably, the upward drift effect of PPEF manifested in our F-layer height data of VT and SO stations with the listed velocities. Plasma uplifts typically enhance the density, while in this case a decrease was observed. The depletion can be attributed to the horizontal plasma redistribution, the arrival of MIT to the latitude of SO and VT. This phase can be clearly observed in isodensity and virtual height data too (Figure 4c-f). The B0 parameter is also sensitive for this type of change, but with not that significant increase in its value. (2) 21:30-02:15 UT (SO) and between 21:52-02:10 UT (VT): Uplift with strong fluctuations with significantly greater F2 heights (890 km vs. 630 km) and speeds (around 90 m/s vs. 31 m/s) at SO and VT, suggesting spatially inhomogene sources like traveling ionospheric disturbances (TIDs) or storm-time meridional wind surges [75]. During this phase, the stations were near the AO (as indicated by the presence of auroral layers), where storm-time winds and TIDs are initiated. The examination of [PERSON] et al. [58] strengthens the presence of MS- and LSTIDs during the main and early recovery phase of this storm. [PERSON] et al. [76] during the analysis of the Halloween 2003 superstorm also identified TIDs which created large plasma depletions. As for the analysis of the different ionosonde parameters, our conclusion is that for the identification of the TID effect, the isodensity data are found to be the best indicator (Figure 4c,d). (3) 03:05-03:50 UT (F2), 03:10-04:25 UT (F1) (SO) and 03:00-04:00 UT (F2), 03:22-05:30 UT (F1) (VT): During this period, the F2-layer uplifted with 145 m/s velocity at SO and 102 m/s velocity at VT. An important difference between the two stations is that at SO the increase in the F2-layer height is not as steady as at VT, but much faster and has three uplift subsections (showing wave-like pattern between 261-546 km, see Figure 4). The steady uplift at VT is also peculiar, since the altitude of the F2-layer rose from 509 to 877 km reaching its highest altitude, thus, the layer went out of the range of the ionograms. In the meantime, the F1-layer at VT and SO descended with velocities of 20 m/s at SO and 32 m/s at VT as it is portrayed in Figure 4e,f. This height decrease was most probably due to the effect of westward DDEF as its presence was registered by [PERSON] et al. [3]. The overall decrease, seen in the F2 density, the Swarm-observed density and Swarm vTEC is the result of the downward drift of the dominant part of the plasma. The anomalous rapid (around 145 m/s at SO and 102 m/s at VT) and steady uplift of the F2 layer at SO and VT may be linked to local heat sources which affect just the F2-layer heights, like frictional heating by subauroral polarization jets streaming along the MIT, or heat downward conducted from ring current (RC) [24]. [PERSON] et al. [68] and [PERSON] et al. [58] proposed that the rapid poleward shift of the EIA (with 450 m/s) together with the equatorward placement of the aurora caused the dramatic ionospheric uplift, which resulted in the prolonged disappearance of the layers at midlatitude during daytime. Note that during this phase, the Dst index was close to its minimum, and the RC to its maximum intensity. This peculiar feature requires further investigation.