## 4 Discussion  
### Spatial Distributions of EQ Precursor  
According to the seismo-ionospheric coupling mechanism, the ionospheric disturbances caused by EQs should not only show time series characteristics but also particular spatial distribution features [26; 27; 28]. Compared with the anomaly information in the longitude direction reported by the previous research, this study pays more attention to the spatial anomaly distribution characteristics in the latitude direction. The reason is that the distance in longitude between adjacent satellite orbits around the EQ epicenter is about 24\({}^{\circ}\) (\(\sim\)2600 km) each day, which is insufficient to monitor longitudinal spatial variations. Although the longitude distance between adjacent tracks in 5 days is reduced to about 4.7\({}^{\circ}\) (\(\sim\)500 km), the time span is too large to detect whole-EQ precursory information. On the other hand, the CSES-01's flight speed is 7.6 km per second, so it only takes tens of seconds to observe hundreds of kilometers in the latitude direction, which can comprehensively investigate the possible pre-EQ anomalies in the flighting orbit area. As shown in Figures 4 and 5, the significant perturbations of \(Te\), \(Ne\), \(No^{+}\), and \(V_{z}\) before Ms 7.1 EQ in Loyalty islands and Ms 6.9 EQ in the southeast of Loyalty islands appeared synchronously in the area 100-200 km northwest of the epicenters, and the spatial extension of these perturbations is about 350 km. According to [PERSON] and [PERSON]'s statistical analysis of the spatial-temporal distribution characteristics of the ionospheric anomalous disturbances before Ms \(\geq\) 6.0 EQs in China [28], the main seismo-ionospheric perturbations do not occur directly above the epicenter locations but shift towards the magnetic equator, which is consistent with these detection results. Moreover, as a known fixed-position high-power artificial source, the impact of the terrestrial very low-frequency (VLF) transmitters on the ionospheric environment could be an important reference for studying the seismo-ionospheric disturbance effect. Figure 11: Same format as Figure 8, but for the variation of the (**a**) \(No^{+}\) and (**b**) \(V_{z}\) detected by the orbit 3806_1 with its revisiting orbits from 15 September to 10 October, which are jointly affected by a strong geomagnetic storm and the Ms 7.1 Papua New Guinea EQ. [PERSON] et al. [14] have presented the observation results when CSES-01 passes above the NAA (44.65\({}^{\circ}\)N, \(-\)67.28\({}^{\circ}\)E, transmission frequency 24 kHz, transmission power 885 kW) and NWC (\(-\)21.82\({}^{\circ}\)N, 114.17\({}^{\circ}\)E, transmission frequency 19.8 kHz, transmission power 1000 kW) stations [29; 30], which are currently the most powerful VLF sources in the northern and southern hemispheres. Under the influence of the ground signal, the plasma parameters (e.g., _Ne, Te, No_+, and \(V_{2}\)) of the ionosphere F layer appear to exhibit significantly synchronous heating disturbances not above the stations but in the corresponding area approximately 205 km south of the NAA station and 220 km north of the NWC station [14], which is very similar to the observed phenomena in this pre-EQ study in Figures 4 and 5. Notably, the abnormal perturbations before Ms 7.4 EQ in Indonesia and Ms 7.1 EQ in Papua New Guinea, as shown in Figures 6 and 7, are located in the area of \(\sim\)100 km southeast of the epicenters, which are opposite to those in Figures 4 and 5. A reason for the difference could be that the epicenter latitudes of Indonesia EQ and Papua New Guinea EQ are lower and are located south of the magnetic equatorial region. As is well known, the fountain effect, i.e., the ionosphere plasma above the magnetic equator, drifts along the magnetic lines to form a double-peak structure, which is the so-called \"Equatorial Ionospheric Anomaly (EIA)\" [31; 32].