## 2 Data and Methods
### CSES-01 Satellite Data  
The CSES-01 satellite was specially developed to detect the abnormal ionospheric disturbances associated with strong seismic activities. It has eight types of scientific payloads that can observe the ionospheric background environment and perturbations in the electromagnetic waves and field, plasma, and high-energy particles. Among them, the PAP and LAP were designed to obtain plasma parameters (ion and electron properties) through in-situ detection. The PAP provides ion density (\(N_{i}\), including hydrogen ion, helium ion, and oxygen ion), ion temperature, and ion drift velocity (\(V_{i}\)). LAP data provides electron density (\(Ne\)) and electron temperature (\(Te\)), respectively. They have a large measurement range that covers the plasma change at \(-\)507 km altitude and high accuracy to discern weak abnormal information. The measurement range of \(Ni\) and \(Ne\) \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**No.** & **Region** & **Date and Time (UTC)** & **Magnitude (Ms/Mw) 1** & **Latitude (\({}^{\circ}\)N)** & **Longitude (\({}^{\circ}\)E)** & **Focal Depth (km)** \\ \hline
1 & Loyalty Islands & 29 August 2018 at 03:51:54 & 7.1/7.1 & \(-\)21.95 & 170.10 & 20 \\
2 & Southeast of Loyalty Islands & 16 August 2018 at 01:03:42 & 6.9/6.5 & \(-\)21.65 & 169.61 & 17 \\
3 & Indonesia & 28 September 2018 at 10:02:44 & 7.4/7.5 & \(-\)0.25 & 119.90 & 20 \\
4 & Papua New Guinea & 10 October 2018 at 20:48:18 & 7.1/7.0 & \(-\)5.70 & 151.25 & 39 \\ \hline \hline \end{tabular} \({}^{1}\) The moment magnitude Mw and focal depth were retrieved from USGS, and the other information was retrieved from CENC.  
\end{table} 
Table 1: Information on the four strong EQs that occurred in southeast Asia and northern Oceania in 2018. Figure 1: Location of the four investigated EQs that occurred in southeast Asia and northern Oceania in 2018. The stars represent the epicenters, and the red lines are the geomagnetic latitude lines. The green star represents the Loyalty Islands Ms 7.1 EQ, and the red star represents the Southeast of Loyalty Islands Ms 6.9 EQ, and the blue star represents the Indonesia Ms 7.4 EQ, and the purple star represents the Papua New Guinea Ms 7.1 EQ. is 5 \(\times\) 10\({}^{8}\)-1 \(\times\) 10\({}^{13}\) m\({}^{-3}\), and _Te_ is 500 K-10,000 K, with a relative accuracy of 10%. The measurement range of \(V_{i}\) is \(-\)3000\(-\)+3000 m/s, with a relative accuracy of 20 m/s [14; 18]. The PAP and LAP onboard CSES-01 operate between latitudes of \(\pm\)65 \({}^{\circ}\), providing 30 or 31 sets of ascending and descending half-orbit data files in the Hierarchical Data Format (HDF) format every day. The PAP samples every 1 s in the whole observation area, while the LAP samples every 1.5 s above China and the main seismic belt around the world, and samples every 3 s in other regions [14; 18]. In this research, we processed the Level 2 standard data of PAP and LAP, which are calibrated physical data with geographic coordinates and time information. It should be noted that the PAP was contaminated after launch, leading to lower absolute values of \(N_{i}\) and larger \(V_{i}\) than the expected ones in the orbit position. After a lot of in-flight commissioning tests and simulation analysis, it was considered that this phenomenon was due to the decrease in the sensitivity of the sensors caused by the contamination layers on the surface of the PAP's sensors. Due to the problems with the absolute values, the PAP data have not been widely studied yet [14]. Nonetheless, the calibration works and some observation results showed that the state of the contaminated layers on the sensors did not change apparently in 2018, therefore, the relative variations of \(N_{i}\) and \(V_{i}\) were stable in a short time, which had the capability of describing the ionospheric anomaly information. [PERSON] et al.