## 4 Discussion
### Difference with Magnetic Storm Anomaly  
The geomagnetic and solar data shown in Figure 2 indicate that several geomagnetic storms occurred from August to October 2018, resulting in a complex ionospheric environment. Based on the data of four seismic candidate anomalous orbits during this period and their revisiting orbits, we compared the different performances of \(No^{+}\) and \(V_{z}\) under the influence of intense geomagnetic storms and strong EQs. As shown in Figure 2, the Dst index on 8 and 10 October in 2018 is lower than \(-30\) nT, and the Kp index is greater than 3, which indicates that a moderate geomagnetic storm occurred on these two days. Furthermore, from Figures 10a and 11a, we can find that due to the influence of a strong geomagnetic storm, the values of \(No^{+}\) in orbit 3775_1 on 8 October and orbit 3806_1 on 10 October in 2018 are far beyond the upper boundaries, about 200-300% higher than the median values, and the affected latitude ranges are as large as more than 40\({}^{\circ}\). Meanwhile, in the local areas of seismic anomaly disturbances, the values of \(No^{+}\) increased significantly based on the influence of the geomagnetic storm, which seems to reflect the combined effects of strong EQs and the intense geomagnetic storm on the ionospheric plasma environment. On the other hand, orbit 2939_1 on 29 August in 2018 and orbit 3458_1 on 28 September in 2018, as presented in Figures 8a and 9a, were not affected by the geomagnetic storm, but they were preceded by a few days of strong EQs. The \(No^{+}\) data did not exceed the upper boundary in such a large range but only greatly enhanced in the local EQ anomaly  
Figure 12: The possible schematic diagram of the plasma perturbation process induced by the seismo-ionospheric coupling. areas that extended for hundreds of kilometers, which increased about 100-200% to the median values. According to previous studies, the seismic anomaly is a regional and local anomaly that is unlikely to cause a global disturbance [21,28]. These observation results are consistent with this view. Based on the data sets obtained from the MICS spectrometer onboard the CRRES satellite, [PERSON] et al. [45] made a statistical analysis of 12 cases of intense geomagnetic storms in 1991. The results proved that oxygen ions (O\({}^{+}\)) in the ionosphere are the main component of the ring current particles during the main phases of intense geomagnetic storms. The increase and decrease of O\({}^{+}\) in the ionosphere are the primary factors leading to the rapid decline and growth of the Dst index during the main and recovery phases of the geomagnetic storm. Although the observation height of the CRRES is higher than the CSES-01, the role of the O\({}^{+}\) in the ionospheric environment could be an important reference for studying the seismo-ionospheric disturbance effect. [PERSON] and [PERSON] et al. [12,14] reported significant disturbances of \(No^{+}\) before Ms7.9 Tonga Islands EQ in 2006 detected by DEMETER satellite and Ms 7.3 Venezuela EQ in 2018 recorded by CSES-01, indicating that \(No^{+}\) is a promising parameter for analyzing seismo-ionospheric perturbation. Therefore, monitoring the relative variation of \(No^{+}\) is important for analyzing the ionospheric anomaly. It is interesting to find that, as represented in Figures 10b and 11b, the trends of \(V_{z}\) in orbit 3775_1 on 8 October and orbit 3806_1 on 10 October in 2018, during the geomagnetic storm, are pretty different from those of \(No^{+}\). \(V_{z}\) is almost within the upper and lower boundaries, and there is no particular change compared with the background trend except for the sudden reverse perturbation over the seismic area, which seems consequently to be related to the incoming strong EQ. The vertical ion drift velocity seems not to be affected by the geomagnetic storm that occurred in the past two days but is susceptible to seismic activities.