## 1 Introduction
Statistical results of superposed epoch analysis have indicated that ULF magnetic anomalies are more likely to appear before sizeable earthquake events rather than after them, especially 6-15 days before the events. Almost one month (18-19 April 1995) before the 13 May 1995 Grevena-Kozani Mw6.6 earthquake, [PERSON] et al. [11] observed anomalous variations of the magnetic field of the Earth, which were mainly recorded in the east-west component. [PERSON] et al. [12] used two modern statistical tools, i.e., ECA and ROC, to revisit the statistical significance of the anomalous changes of the Earth's electric and magnetic field as precursors to earthquakes. They studied two independent datasets (first, electric field data from Greece since the 1980s and second, magnetic field data from Japan during 2001-2010, which is alternatively termed ULF seismo-magnetic phenomena) and found that they exhibit precursory information far beyond chance. The above studies were all performed involving the polarization method or magnetic field data in the ultralow frequency with ground data before or after earthquakes. Space science is also increasingly emerging with the rapid development of science and technology. The Soviet Union and United States have launched a series of electromagnetic satellites, obtaining global high-precision and high-resolution information of the geomagnetic field and ionosphere since the middle of the twentieth century [13; 14]. Magnetic measurements from space began with the satellite era and the launch of Sputnik 3 in 1958 [15]. At low Earth orbits (LEO), progress was next gradually achieved from a series of missions, for example, POGO, Magsat [16], Orsted [17], CHAMP [18] and SAC-C [19]. Exploration of Earth's magnetic field has always been at the forefront of science and applications. France launched the DEMETER electromagnetic satellite in 2004, focusing on seismic and volcanic electromagnetic effects [20]. The European Space Agency (ESA) launched the Swarm satellites, realizing joint multisatellite probing of geomagnetic field and plasma parameters in the low earth orbit (LEO) region with an accuracy of 0.3 nT in the total field and 1 nT in the vector field in 2013 [19; 21; 22]. Electromagnetic satellites have widely stimulated interest in the study of seismic ionospheric disturbances due to their specialized orbit design, global coverage characteristics, high precision and multiparameter electromagnetic measurement technology. This topic has become a new hot spot in the field of earthquake monitoring and prediction [23]. [PERSON] et al. [24] detected magnetic anomaly signals in the ionosphere prior to an earthquake with three-component data of the magnetic field provided by Swarm satellites. They found that the anomaly of the horizontal Y-component was more pronounced than that of the other components. [PERSON] et al. [25] determined that the three components of the magnetic field and electron density anomalies occurred \(\sim\)40 days before seismic sequences in the center of Italy from 2016 to 2017 based on Swarm satellite data. Moreover, the satellite-recorded anomalous variations coincided with the variations in related parameters of the Earth's surface and atmosphere; thus, time-series anomalies from the Earth's surface to the ionosphere could be observed. This may support the possibility of developing models for lithosphere-atmosphere-ionosphere coupling (LAIC) purposes. They also concluded that there existed anomalies of the horizontal Y-component of the satellite data instead of the other components. In addition, [PERSON] et al. [26] argued that the geomagnetic horizontal Y-component was less affected by external perturbations and could be employed to detect anomalous sources in the Earth's interior better than the other two components. [PERSON] et al. [27] proposed a new method to analyze earthquake-related space magnetic field perturbations based on magnetic field data from Swarm satellites.