This study uses the global ionospheric total electron content （TEC） grid data provided by the US Jet Propulsion Laboratory （JPL） of the IGS Center. Based on geographic coordinate information, the closest TEC grid data closest to the M_S5.7 earthquake in Jilin Songyuan （45.27°N, 124.71°E） in 2018 was selected for calculation and analysis. Since ionospheric anomaly regions before an earthquake are not all concentrated above the epicenter, they also occur in regions at a certain distance from the epicenter, Therefore, the research grid points were selected from the 9 closest grid points around the epicenter.

Through comparative calculation of the traditional quartile method and the sliding quartile method, it is determined that the sliding quartile method is less affected by special phenomena than the traditional one when calculating the results. It more objectively reflects the actual background of the observation points, yields more distinct results, and is consistent with the previous studies. Time series analysis of the four study grid points closest to the Songyuan earthquake epicenter using the sliding quartile method shows that the impact of polar substorms on ionospheric observations （on −11 d and −5 d relative to the earthquake） can be eliminated. The ionospheric observations first increase （−14 d to 8 d） and then decrease （−8 d to 1 d） in the week before the earthquake, consistent with the study by Wang et al （2014）. Meanwhile, the amplitude of ionospheric anomalies increases as epicenter distance decreases. Located further north, Songyuan is more affected by the polar magnetic substorms. After excluding space weather effects, there is a high probability of five days of positive and two days of negative ionospheric anomalies related to the earthquake.

The analysis of seismic ionosphere spatial distribution anomalies shows that: ① The closer northern ionospheric disturbances are to the intense phase of polar substorms, the stronger the disturbances become; ② Pre-earthquake TEC observations first increase, then decrease, and rise again post-earthquake, with anomaly amplitude increasing as epicenter distance decreases. ③ In terms of ionospheric spatial distribution, positive and negative anomalies are temporally concentrated and regular, with an overall "N"-shaped pattern. Anomalies over and near the epicenter lasted more than two hours, featuring a small area and low intensity but obvious localization.

A lithosphere-atmosphere-ionosphere coupling （LAIC） mechanism governs energy propagation during seismic gestation and occurrence. Combining analysis of deep lithospheric resistivity, atmospheric and ionospheric data for the Songyuan earthquake, a close correlation between the three spheres is found during the gestational period and coseismic period: lithospheric medium fracturing, energy release and electrical changes exert a radiative effect on the atmosphere and ionosphere. Negative ionospheric TEC anomalies are likely directly related to atmospheric electric field changes caused by negative charges released during rock rupture and upward electron transport via the vertical atmospheric electric field. Positive TEC anomalies mainly result from positive charge release in rocks, which accelerates atmospheric ion collisional ionization and alters ionospheric ion density distribution. The atmospheric thermosphere and ionosphere also exhibit mutual influence and synchronous variations-particularly, high positive ionospheric TEC anomalous are well synchronized with atmospheric thermal infrared anomalies in terms of intensity enhancement and distribution morphology.

Currently, pre-earthquake ionospheric detection applications in China are mainly concentrated in western region of M_S≥6.0 earthquakes, with few studies in eastern China （fewer and weaker earthquakes）. In recent years, Songyuan has become one of the most seismically active areas in Northeast China. This study analyzes the largest Songyuan earthquake in the past five years: the May 28, 2018 M_S5.7 Songyuan earthquake in Jilin Province on （epicenter depth of 10 km）. It presents the application of a short-term ionospheric TEC prediction method in Songyuan, supplementing eastern China seismic data for ionospheric anomaly-based seismic prediction and accumulating experience for pre-earthquake ionospheric detection application.