# Retrospective Study on Seismic Ionospheric Anomalies Based on Five-Year Observations from CSES
## 3 Results
### Summative Analysis
\begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{**Global Shallow EQs with \(\mathbf{Ms\geq 7}\) and Depth \(\leq\) 100 km**} \\  & **The Number of EQs Analyzed** & **The Number of EQs with Anomalies** \\ \hline SCM & 38 & 27 \\ EFD & 32 & 23 \\ HPM & 47 & 24 \\ PAP & 38 & 9 \\ LAP & 38 & 28 \\ GOR & 32 & 15 \\ HEPP & 38 & 22 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The number of EQs with anomalies compared to all EQ cases analyzed by seven payloads onboard CSES-01. Figure 8: The anomaly recognition rate to global shallow strong EQs (Ms \(\geq\) 7 and depth \(\leq\) 100 km) of each payload onboard CSES-01. of EQs with certain anomalies recorded by different payload groups. The red percentage marks the proportion of the number of earthquakes observed. We conclude the following:  
* For over 90% of these 47 strong shallow EQs, certain anomalies were captured by at least one payload onboard CSES-01;
* For more than 65% of these 47 strong shallow EQs, two or three payloads onboard CSES-01 could simultaneously record the ionospheric anomalies before the mainshock. Among them, 45% of these EQs exhibited anomalies that were concurrently recorded by three payloads, while about 21% of these EQs displayed anomalies detected simultaneously by two payloads;
* For about 4% of these EQs, five or more payloads recorded disturbances related to the EQs. In addition, we summarized the most sensitive parameters to EQs of each payload and their respective spatiotemporal distribution characteristics of anomalies, as presented in Table 3. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Payload**} & **The Sensitive** & \multirow{2}{*}{**Abnormal Phenomena**} & **Anomalies Occurring** & **Anomalies Occurring** & **Anomalies Occurring** \\  & **Parameter** & & **Time** & **Position** \\ \hline \multirow{3}{*}{SCM} & Waveform and & Positive anomalies with & 5–10 days, 20–25 days & \\  & spectrum in the & a change amplitude & before the EQ, and on & \\  & ULF band & exceeding 20\% & the mainshock day; & \\ \hline \multirow{3}{*}{EFD} & Waveform and & Positive anomalies with & 5 days before the EQ, & \\  & spectrum in the & more than 2\(\sigma\) of & 10–15 days and 20–25 & \\  & 19.5–250 Hz band & variation & days before the EQ & \\ \hline \multirow{3}{*}{HPM} & East component of the & Magnetic disturbance & From 4 days before the & \\  & magnetic field & of 2–3 nT & EQ to the day of the EQ & \\ \hline \multirow{3}{*}{PAP} & \multirow{3}{*}{\(N_{Q\leftrightarrow}\),} & Positive abnormal & \multirow{3}{*}{1–5 days before the EQ} & \multirow{3}{*}{Southwest of the} \\  & & disturbance of \(N_{O+}\) & & \\ \cline{1-1}  & \(N_{O+}\), & with over 50\% change & \multirow{3}{*}{1–5 days before the EQ} & \multirow{3}{*}{Southwest of the} \\ \cline{1-1}  & Vertical drift velocity of & amplitude; & Both positive and & \\ \cline{1-1}  & & negative perturbations & & \\ \cline{1-1}  & & of \(Vz\) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Seismic-ionospheric anomalies and their spatiotemporal distribution observed by CSES-01. Figure 9: The proportional distribution of synchronization anomalies from multiple payloads for each earthquake (EQ) case. Regarding electromagnetic fields, anomalies mainly manifest in the ULF and ELF bands. For ionospheric plasma parameters, fluctuations in plasma density are more frequently observed, whereas changes in plasma temperature are less common. The anomalies observed by EFD and SCM are often synchronized in time and position; the anomalies of ionospheric plasma parameters usually appear later than those in the electromagnetic field, while energy particles are closer to the time of EQ occurrence. 2. The majority of the abnormal variations detected by payloads exhibit positive anomalies, or, in other words, show enhancement phenomena. 3. The occurrence times of anomalies are predominantly concentrated in three periods: the mainshock day, within 7 days, or 11 to 15 days before the mainshock.