## 5 Discussion  
Two large EQs, the Maduo \(M_{\text{S}}\) 7.4 EQ on 22 May 2021 and the Menyuan \(M_{\text{S}}\) 6.9 EQ on 8 January 2022, were successfully recorded since the data of the CSES satellite were put into service for EQ prediction work on the Chinese mainland at the end of April 2020. Some useful information was found when we looked back at these processes. Obvious ionic variations, as well as electronic anomalies were found two weeks and one week prior to both events, which is highly coincident with the conclusion attained by previous investigations. In addition, the distance between the epicenter of the EQ and the ionospheric anomaly was about 600 km for the Maduo event and 120 km for the Menyuan event, which was well within the distance estimated using the Dobrovolsky formula R = 10\({}^{0.4\text{M}}\), where R is the radius of the EQ preparation zone, and M is the EQ magnitude [35]. The fact that electromagnetic (EM) emissions accompany every stage of some large earthquake preparations seems undebatable, although short-term earthquake prediction is still one of the most challenging targets in earth science today [19]. As the development of satellite Earth observation (EO) continues, there is an increasing amount of evidence that during some of the last stages in the long-term process of preparation, there could be a transfer of energy between lithosphere, atmosphere, and ionosphere, so as to introduce the concept of a lithosphere-atmosphere-ionosphere coupling (LAIC) among the three involved layers of the Earth [36; 37; 38; 39; 40]. However, the producing and propagating mechanism of seismo-electromagnetic signals, also as an energy origin of LAIC, has always been a controversial issue since seismic-related electromagnetic emissions have been reported. It basically includes a chemical channel [41; 42; 43], acoustic channel [44; 45; 46], electromagnetic channel [4; 38], etc. [PERSON] et al. [4] qualitatively specified an LAIC model before the Wenchuan event by analyzing parameters from ground-based observations to space-born observations: electromagnetic energy propagated from the epicentral area, via the atmosphere and ionosphere, to the equatorial plane, and through this plane, finally, to its magnetically conjugated area in the opposite hemisphere. However, this evidence remains far from a correct prediction for an impending EQ. Firstly, we cannot specify the right location where a forthcoming event will happen in light of the anomalous area. The Maduo EQ this time, for example, was 600 km away from  
Figure 11: Fluctuations in **(a)** He\({}^{+}\) and O\({}^{+}\) densities and **(b)** electron density registered by the CSES satellite on 2 January 2022, 6 days before the Menyuan \(M_{\text{S}}\) 6.9 EQ. Obvious variations related to this Menyuan event are labeled with black arrows. the ionospheric anomaly. It has been reported that the GPS TEC (total electron content) abnormity lay in the southeast 15-20\({}^{\circ}\) away from the epicenter of the Wenchuan \(M_{\rm S}\) 8.0 EQ on 12 May 2008 [47]. At the same time, a large EQ can induce ionospheric influence around its epicentral area, as well as in its magnetically conjugated point area, which also leads to much difficulty in confirming the correct location of a forthcoming event. Concerning the spatial distribution of ionospheric variations, various amplitudes of the ionospheric parameters are usually considered. Previous studies have shown that the maximum affected area in the ionosphere does not well coincide with the vertical projection of the epicenter of an impending EQ [5] and is shifted towards the equator in high and middle latitudes [48]. This feature can be thought as enhancements of the EIA (Equatorial Ionization Anomaly) strength as reported by [PERSON] et al. [49]. These results seem in agreement with the observations performed by [PERSON] et al. [50] before the Wenchuan \(M_{\rm S}\) 8.0 EQ with TEC data.