## 5 Conclusions  
This strong magnetic storm from 25-29 August in 2018 can be divided into three phases, the main phase with a fast decrease in SYM-H index from 25-26 August; the quick recovery phase with a quick increase in SYM-H during the last half of the day on 26 August; the slow recovery phase from 27-29 August. Based on the multi observations from CSES and other satellites, some interesting ionospheric characteristics at medium and low latitudes can be concluded as the following, responding to the three magnetic storm phases.  
1. Typical penetration signals of electric field were illustrated during three storm phases from the ultra-low frequency band to very low frequency band in either local daytime or nighttime from CSES. Ne showed strong correlation with electric fields in extremely low frequency bands under 1125 Hz in local daytime at 0-30\({}^{\circ}\) N and 15-45\({}^{\circ}\) S in the nightside during the main phase, while in the recovery phase, the high positive correlation between electric fields and Ne were concentrated at 0-15\({}^{\circ}\) S, 45-60\({}^{\circ}\) S in the dayside, and in the nightside 30-45\({}^{\circ}\) Swhere the penetration of electric fields and enhanced Ne were concentrated at. The interaction of electric fields with ionospheric electron density decreased in the nightside both at the main phase or recovery phase, compared to in the dayside.
2. High solar speed generated significant effects during the recovery phase, especially the nighttime ionosphere, with lower Ne in 27-28 August at low latitudes. Higher negative correlation occurred with r \(<-0.5\) of speed/TEC in the nightside during the recovery phase, while solar wind pressure contributed less during the recovery phase with r \(<0.4\) than those in main phase with r \(>0.6\).
3. Multi observations reveal the local time dependence of Ne and TEC to this magnetic storm, with four local time variation modes presented. The depletion of Ne is much  
Figure 10: The electron density (**a**) and electron temperature (**b**) from Swarm-A in local nighttime during 24 to 29 August in 2018.  
clearer at low latitudes in local daytime at a fast recovery time on 26 August, but it is obvious at medium and low latitudes in local nighttime during the slow recovery time of 27-29 August. The electric field observations from CSES in the dayside of 14 LT and the nightside of 02 LT demonstrated the strong penetration electric at middle and low latitudes in extremely low frequency and very low frequency both in the main phase and recovery phase, but some regions still exist with a correlation r < 0.1, which was also revealed in many small r values of speed and pressure with TEC. The regional ionospheric response needs to consider the local plasma and neutral particle environment, as suggested in other research.  
Data curation, X.Z., L.D. and L.N.; Formal analysis, X.Z.; Investigation, L.D.; Methodology, X.Z. and L.N.; Writing--original draft, X.Z.; Writing--review and editing, X.Z. All authors have read and agreed to the published version of the manuscript.  
This work was funded by the National Natural Science Foundation of China (NSFC) under Grant Agreement No. 41674156 and the National Key R&D Program of China under Grant No. 2018 YFC1503506.  
This study does not require ethical approval.