## 5 Discussion  
If there is a perturbation source stemming from an earthquake, the vertical component of the geomagnetic field should be drastically perturbed regularly, while most of the horizontal components of the geomagnetic field should be slightly perturbed [6; 7; 10; 31]. In contrast, if there is a perturbation source stemming from the space environment, there should be obvious changes in both the horizontal and vertical components (Figure 12). The geomagnetic pulsations during nighttime are Pi2 and Pc4 and others, which are known to be usually horizontal component [32]. But, if the source of emissions is situated under the ground, we can expect the polarization ratio (the ratio between vertical component Z and horizontal component H) >1, which is found by [PERSON] et al. [33] using the experimental measurements and also by [PERSON] and [PERSON] [4] based on theoretical considerations [5]. Therefore, the phenomenon of perturbation changes in the geomagnetic three-component data recorded by the HPM onboard the CSES and ESA Swarm satellites before and after earthquakes, with drastic perturbations of the horizontal component and slight perturbations of the east-west component, must be further described and investigated. Figure 12: Geomagnetic polarization mechanism model. The ionosphere produces an ionospheric equatorial anomaly during the daytime, where the daytime eastward electric field in the E layer (produced by thermal wind drive) can be mapped along magnetic lines to the F layer due to the high parallel conductivity along these magnetic lines. The eastward electric field along the magnetic equator causes plasma to drift upward through E \(\times\) B. As the plasma rises, it is subjected to gravity and pressure gradient forces that cause it to spread out along the force magnetic lines toward either side of the magnetic equator. The plasma exhibits fountain-like movements under the action of electric field drift and diffusion, referred to as the fountain effect, causing the plasma along the magnetic equator to move toward the geomagnetic latitude of \(\sim\)\(\pm\)15\({}^{\circ}\), forming a double-peak structure (equatorial ionization anomaly (EIA) crests). The EIA phenomenon disappears at night [34]. LAIC models are roughly categorized into three propagation pathways, including additional DC electric field models and acoustic gravity wave and electromagnetic wave propagation models, each of which induces ionospheric plasma changes in the ionosphere [23]. The CSES flies at an altitude of \(\sim\)500 km and detects physical parameters related to the F layer of the ionosphere. If the plasma in the D and E layers of the ionosphere near the epicenter, affected by an earthquake, rises to the F layer, it is subjected to gravity and pressure gradient forces, causing the plasma to spread out toward the poles along the force magnetic lines, thereby generating currents along this direction. Then, a change in the horizontal component of the magnetic field is produced, and this physical process could explain the obtained conclusions, i.e., [PERSON]'s law. The parameters detected by the PAP payload are considerably perturbed before earthquakes [35; 36]. To verify the physical mechanism, we studied ion velocity Vx data recorded by the PAP payload onboard the CSES associated with the western orbital group near the epicenter from May to July 2019 (the Vx velocity direction matches the direction of the satellite flight velocity). We selected the up-orbit data, so the satellite flight direction was toward the geographic North Pole. Therefore, the Vx velocity perturbations direction was toward the poles. It was found that the Vx data recorded during the 21 May orbit approximately a month before the earthquake began to exhibit perturbations near the epicenter, which occurred in the same region as the horizontal perturbations of the magnetic field recorded by the HPM, both occurring near 43\({}^{\circ}\) N at the same time (Figure 13).