## 3 Results
### On the Occurrence of the Ionospheric Storm Effects  
The occurrence of ionospheric storm effects is subject to several dependences for which the regular thermospheric winds play a key role. As an example, one may note the seasonal dependence: when storm-induced wind flow coincides with the direction of the prevailing meridional wind, which is the case for summer, the neutral composition disturbance zone penetrates to relatively low latitudes, and negative storms can also be observed at lower latitudes. On the other hand, in winter, the prevailing wind contrasts with storm-induced wind and, therefore, negative storm effects remain confined at higher latitudes to make positive effects the predominant feature of wintertime ionospheric storms [24; 25; 26; 28]. Another key feature in the ionospheric storms occurrence is their dependence on local time. Neutral composition changes tend to be larger and extend to lower latitudes in the early morning sector. This is in agreement with the argument that the disturbance transport takes place in this sector due to the reduced ion drag and coincidence of the equatorward regular wind with storm-induced wind flow. In this respect, negative storm effects at middle latitudes are mainly observed during nighttime hours. While rotating into the daytime sector following the Earth's rotation, the disturbance zone is partially recovered and pushed back by poleward-directed daytime regular winds, but it is still able to produce daytime negative ionospheric storm effects. On the other hand, positive storm effects tend to occur in the daytime hemisphere, particularly in the prenoon and afternoon sectors [24, 25, 28]. Figure 2 provides an example of how positive and negative storm phases may alternate in different local time sectors and/or latitudes. For a more representative view of the ionospheric response to this intense storm event, the reader can refer to several research articles available in the literature, e.g., [31, 32, 33]. Multi-instrument data analysis and physics-based model simulations are also carried out for other intense storm events that occurred in solar cycle 24, e.g., [34, 35, 36] provide the most recent evidence on the progress achieved in our present understanding, but also on the complexity that one may face in practice. Indeed, the sequence of ionospheric storm effects may be very complicated as several different processes work in concert, and the ionospheric response to each storm is determined by a unique and complex interaction of drivers, while multiple and/or successive intensifications of the geomagnetic activity may further complicate the interpretation of the observed effects, e.g., [37]. It has also been suggested that ionospheric storm effects are subject to solar cycle dependence. At the beginning of the 2000s, this argument was only based on model predictions. For instance, [PERSON] et al. [38] found that, considering winter conditions, both the magnitude and extent of composition perturbations were larger during solar minimum, suggesting that disturbance effects are transported more efficiently out of the polar region into middle latitudes during these conditions. Interest in the solar cycle dependence of the ionospheric storm time response was greatly revived in the years following the deep 2008-2009 solar minimum, and probably the low activity solar cycle 24. Some indicative results came from identified shortcomings in ionospheric prediction capabilities during this deep solar minimum, under certain conditions that apply to all model formulations, from empirical to physics-based ones. For instance, [PERSON] et al. [39], in an investigation of the ionospheric disturbances under low solar activity conditions in 2008-2009, pointed out that the STORM model [40, 41]--incorporated into the International Reference Ionosphere (IRI) standard model--did not provide reliable predictions for the peak electron density during CIR-generated storms. [PERSON] et al.