## 3 Data Analysis
### The Perturbations in Electron Density and Temperature from CSES  
In Figures 4 and 5, we plotted Ne and Te from LAP onboard CSES from 25 to 29 August in local daytime and nighttime individually. In dayside of 14 LT, the peak Ne was quite clear at latitudes of 0-20\({}^{\circ}\) N. During the main phase of this magnetic storm on 25-26 August, the equatorial peak Ne was further enhanced and spread to \(-20^{\circ}\) S and \(40^{\circ}\) N (Figure 4a). Then, Ne decreased abruptly to about \(10^{10}/\mathrm{m}^{3}\) during the last half of the day on 26 August and increased again from 27 to 29 August, with some larger values above \(10^{11}/\mathrm{m}^{3}\) at latitude of \((-20)\)-\(0^{\circ}\) in the southern hemisphere (Figure 4a). As for Te in Figure 4b, it varied reversely with Ne at the equatorial region, with strong decreases of about 1000 K at the main phase of this magnetic storm on 25-26 August and significant increases of above 3000 K in the northern hemisphere, with the decreasing Ne in last half of  
Figure 3: The electric field spectrum values at 6 frequency bands ((**a**): 225 Hz; (**b**): 725 Hz; (**c**): 1125 Hz; (**d**): 7500 Hz) in local nighttime from 25 to 29 August in 2018.  
the day on 26 August. From 27-29 August, the equatorial Te nearing 1000 K was still lower than that of about 1500 K during the quiet first half of the day on 25 August, and the Te valley spread to the southern hemisphere as peak Ne at the equatorial area during all these disturbed days. In nightside of 02 LT, as shown in Figure 5, peak Ne values were located at 20-40\({}^{\circ}\) at both hemispheres, partly at the equatorial area, which is largely different with those in the local daytime in Figure 4. To reveal the background information, one more day on 24 August was included in Figure 5. It can be seen that, during this magnetic storm, Ne was enhanced mainly on 26 August between the latitude of \(\pm\)40\({}^{\circ}\), with the simultaneous decrease in Te at the same region. Another interesting phenomenon in local nighttime is the regular daily Ne valleys with a clear boundary at mid latitudes of 40-65\({}^{\circ}\), also known as the midlatitude trough, where Ne decreased at least one order of magnitude relative to the Ne around latitudes of 30\({}^{\circ}\), typically in the southern hemisphere during the whole studied time period. To illustrate the changes in the position of the midlatitude trough of Ne, Table 1 listed the latitudes of the first Ne minimum, near to equator-side in the northern and southern hemisphere in UT06-08 and 18-20, where \"/\" represents that the minimum was still not occurring in the observational scale of CSES, within a latitude of 65\({}^{\circ}\). During  
Figure 4: The electron density (**a**) and electron temperature (**b**) in local daytime from 25 to 29 August in 2018. Figure 5: The electron density (**a**) and electron temperature (**b**) in local nighttime from 24 to 29 August in 2018.  
this storm, the latitudes of Ne trough in the southern hemisphere moved inside \(-60^{\circ}\) S at the beginning of 26 August when it should be beyond \(-65^{\circ}\) S at the same time period in other days, and the northern latitude was 33.24\({}^{\circ}\) N, moving 20\({}^{\circ}\) to the south relative to 24 August at 53.54\({}^{\circ}\) N and about 15\({}^{\circ}\) relative to that on 25 August at about 48.65\({}^{\circ}\) N. The obvious trough region in Ne maintained from 27-29 August, and its top equatorward minimum boundary was closer to 41\({}^{\circ}\) latitude in the southern hemisphere, being 5-8\({}^{\circ}\) to the north compared with those on 24-25 August (Table 1). Compared with the electric field at 225 Hz and 7500 Hz in Figure 3a,d, the Ne trough at latitudes of 50-65\({}^{\circ}\) was just corresponding to the strong disturbed region in ELF/VLF electric field, illustrating the significant correlation in both parameters. Te in local nighttime showed an obvious peak structure at a latitude of 40-65\({}^{\circ}\), in contrast with Ne.