## 4 Results
### Multi-Parameter Comparisons  
The lithosphere-atmosphere-ionosphere is an open and coupling system; the electromagnetic emissions and the chemistry gases emitted by the stressed rocks in the EQ preparation zones lead to the variation in geophysical and geochemical field, thus directly impacting the ground-based instruments. The seismic signals can also couple into the atmosphere, breaking the chemical reaction balance in there, leading to the formation of local electric currents, air ionization, atmospheric gas condensation, and plasma parameter irregularity [10]. Therefore, in addition to CSES data, the CSES scientific application center also collects multi-source data. At present, the multi-source observations from infrared/hyperspectral remoting sensing satellites, ground-based electromagnetic field instruments, the vertical/oblique ionosonde, and ground-based GNSS receivers etc. can be collected for the first time to comparatively explore the seismic signals with the CSES data. Figure 5: The abnormal ULF waves emitted before the 2021 M 8.1 and M 7.0 EQs in Alaska. We pay considerable attention to the atmospheric parameters because the gas released from the crust can effectively change the conductivity condition of the atmosphere, thus leading to a series of coupling processes in the lithosphere-atmosphere-ionosphere [10]. Previous studies have suggested that the atmospheric parameters, such as the radon, methane, aerosol optical depth (AOD), skin temperature (SKT), and surface latent heat flux (SLHF), are sensitive to seismic activities at different stages of the EQ preparation process and can respond sooner to the seismic precursors [33; 34] than the seismo-ionospheric parameters. For example, Figure 7 shows the variation in the methane concentration from 2016 to 2021 (provided by the NASA Goddard Earth Sciences Data and Information Services Center) over the Alaska EQ area. Compared with the variation trend from 2016 to 2020, the CH4 concentration increased significantly on 11 July 2021 (18 days before the M 8.1 mainshock), then fell to a low level where the M 8.1 shock occurred; after that, it started to rise to a new peak where the second shock M 7.0 occurred, and the CHR concentration continually decreased and fell back to the background trend level after September 2021. Figure 8 shows the spatial distribution of the 8 days averaged AOD values (provided by AQUA MODIS C6 of NASA) in 2021 relative to the background field calculated by data from 2001 to 2020 over the Alaska earthquake area. The AOD values became enhanced from 26 June to 21 August, especially in the 8 days time windows of 26 June to 3 July, 28 July to 4 August, and 13 August to 21 August; the AOD is significantly increased relative to the background. The significant enhancements mainly appeared in the southern part of the earthquake epicenter. Figure 6: The magnetic field disturbances in frequency from 60 to 73 Hz relative to the background map revealed by the PSD values of the variant magnetic field recorded by SCM during the 29 July 2021 M 8.1 and August 14 M 7.0 Alaska EQs. The star denotes the epicenter location. The TEC data also easily became disturbed over the forthcoming epicenter regions, showing a significant decrease or increase within one week before the mainshock [35]. Figure 9 shows the vertical TEC anomaly over the Alaska EQs, extracted from the global ionospheric map (GIM) published daily by the International GNSS Service (IGS). The green curve presents the median values of TEC data over the Alaska epicenter zone, and the grey lines are the upper and lower boundaries computed by the IQR method in Section 4.2. The red curve shows the current TEC observations. The red and black bars are the difference values between the red and green curves. It can be seen that the continuous positive anomaly appeared before the July 29 M 8.1 EQ, followed by a negative anomaly after the mainshock. However, it is difficult to identify any apparent anomaly during the August 14, M 7.0 EQ.