## Data and Methods
### Data Preprocessing and Background Field Construction  
The original profile database involved no quality control. Due to meteorological, instrument quality, and other factors, some irregular RO profiles were inevitable and controlled. First, the unqualified data with strong fluctuation were removed; for the detailed preprocessing, see Appendix A. For the final-presented analysis, around 20,000 observations were classified for the next procedure of constructing the Nmf2 model. The common calculation method of the ionosphere's spatial distribution reference value includes a COSMIC empirical model value but usually needs to use long-term data [29]. Another method is to establish the global or regional model of electronic density quickly before the earthquake, after preprocessing RO profiles from COSMIC occultations. A kriging interpolation method was used here to obtain the fast Global Nmf2 maps. This technique can yield valuable information about the ionosphere's behavior and its evolution, with particular attention paid to the evolution of spatial gradients [30; 31]. The ionosphere parameter (e.g., TEC and Ne) had been previously kriging interpolated and drawn mainly with the combination of ground-based techniques. [PERSON] et al. [32] firstly introduced the data of only 14 GNSS stations to elaborate TEC maps over Europe with a time rate of 1 h. Furthermore, [PERSON] et al. [33] proved the possibility of constructing a 3-D electron density region by a simple kriging approach. Regardless of the reconstructed TEC or electron densities, promising improvements have been achieved through the validation of the ionosondes Ne and GNSS TEC [34]. The method can not only solve the problem of overly sparse sampling, especially in situations of data scarcity but also give the estimation deviation of each point. To detect the seismic-ionosphere disturbed signals, we constructed the Nmf2 models in a short period before an earthquake by the kriging interpolation algorithm. For more specific operations, please see Appendix B. Following the usual representation of the global ionospheric map such as IGS GIMs and IRI GNMs, these file products are provided with the Geographic Frame Coordinate System. However, inevitably, changes in the TEC or Nmf2 maps are influenced by the factors of the earth's rotation, the earth's pole moving, etc. If their strategy is adopted, the data sparsity of the ionosphere retrieved from the COSMIC constellation will greatly affect the result's reliability (see Supplementary Figure S1). In this paper, we introduce an Inertial Coordinate System of the Geomagnetic Sun-fixed Frame Coordinate System (local time and geomagnetic latitude). In the sun-fixed coordinate system, where the impact factors of the earth's rotation and the earth's pole moving are ruled out, the diurnal variation of the ionosphere tends to be stable (see Supplementary Figure S2). Therefore, the data of the ionosphere Nmf2 are easily modeled [12]. We first extracted the COSMIC Nmf2 data within 15 days before the global earthquake and divided the data in a day into 12 periods, with 2 h as the time interval. The data were then classified in the same period into the geomagnetic sun-fixed coordinate system, forming a total of 12 ionosphere GNMs based on kriging interpolation. After constructing the Nmf2 models, the observation value was taken as the inspection value to compare its variations with the ionosphere's normal state. The deviation degree between Nmf2 observations and model values is expressed as follows:\[\delta=\left|\frac{NmF2_{obs}-NmF2_{\text{model}}}{NmF2_{\text{model}}}\right| \tag{1}\]  
where \(NmF2_{obs}\) and \(NmF2_{\text{model}}\) represent the observation value and GNM value, respectively. According to the deviation degree with a large \(\delta\) value, some irregular electron density profiles may exhibit a damaged structure. Such profiles may also occur inside ionospheric storms or be caused by medium/small-scale irregularities [34].