## 4 Discussion on the Corresponding Processes in Ionosphere
### The Movement of Midlatitude Trough during the Magnetic Storm  
On the basis of the DEMETER satellite in local nighttime around 22:30 at the altitude of 670 km during 2006-2009, [PERSON] et al. [47] studied the midlatitude trough and the plasmapause in the ionosphere by using Ne, Te, and whistler counts, respectively, and their statistical results illustrated that both of them moved equatorward during the magnetic disturbed conditions, while the midlatitude trough would occur in the equatorward side of the plasmapause when Kp \(\geq\) 6. Onboard CSES, no whistler data was automatically detected in electric field as DEMETER to determine the position of the plasmapause, so only the midlatitude trough will be discussed here, based on the observations of Ne and Te from LAP. As shown in Figure 5, the nighttime midlatitude trough can be clearly distinguished in both hemispheres at the altitude of the CSES at about 507 km, with a decrease in Ne and an abrupt increase in Te beyond a latitude of 40\({}^{\circ}\). During this magnetic storm on 25 August, the daily northmost point of the midlatitude trough boundary moved about 5\({}^{\circ}\) northward in the southern hemisphere, relative to that on 24 August. On 26 August, the daily southmost point of the midlatitude trough reached a latitude of about 30\({}^{\circ}\) N in the northern hemisphere, while the southmost boundary in the southern hemisphere drifted to a latitude of \(-50^{\circ}\) S, where it was always beyond \(-65^{\circ}\) S at normal conditions in the first few hours on 24 August and 25. Therefore, the troughs all shifted their position of 15\({}^{\circ}\) to the equator at both hemispheres. During the recovery phase in 27-29 August, the northmost latitude of the southern trough maintained at about \(-40^{\circ}\) S, with equatorward movement of about 5\({}^{\circ}\) relative to that on 24 August. In the northern hemisphere, the northmost boundary of the trough moved from 65\({}^{\circ}\) N to 55\({}^{\circ}\) N in 26-27 August, being still at 60\({}^{\circ}\) N in 28-29 August. Therefore, during the whole event, the local nighttime midlatitude trough observed from CSES shifted equatorward about 15\({}^{\circ}\) at the main phase with the biggest Kp = 7 and maintained a 5\({}^{\circ}\) equatorward movement during the recovery phase for more than three days. Figure 10 presented the local nighttime Ne and Te on Swarm-A, in which the boundary of the midlatitude trough was quite clear, especially its topmost part at a high latitude of 60-70\({}^{\circ}\) N in the northern hemisphere, due to its global coverage. In the southern hemisphere, no high values of Ne occurred again at a high latitude beyond 60\({}^{\circ}\), so this midlatitude trough covered quite a large area, even to \(-90^{\circ}\) S, which is totally different compared to that in the northern hemisphere. Compared with the results from [PERSON] et al. [48] by using COSMIC observations, the large covering area of the trough in the southern hemisphere should be related to its seasonal variations of lower Ne in winter days. Around this magnetic storm, Swarm-A exhibited the same characteristics with CSES in the midlatitude Ne trough and Te peak, with significant equatorward movement of more than 15\({}^{\circ}\) at the main phase and maintained a small shift of about 5\({}^{\circ}\) during the recovery phase in the local nighttime. As for the shift of the midlatitude trough, [PERSON] et al. [49] introduced an empirical model to qualitatively interpret the dynamics of the position of the trough at 430 km altitude during the main phase, and their results showed step-like equatorward movement in the pre-midnight hours in the main phase of an intensive magnetic storm, while the solar local time and magnetic local time were considered and compared in the new model due to the dependence of the trough on them [50].