## 4 Discussion  
The generation of earthquakes is an extremely complex process that usually involves the combined effects of multiple factors. Consequently, the effects of earthquakes on the ionosphere are often multi-faceted. A model proposed by [PERSON], namely, the LAIC model, suggests that seismic disturbance can spread from the lithosphere to the atmosphere and ionosphere via electromagnetic, acoustic, and geochemical pathways [56]. The physical processes, crustal movements, and rock ruptures that result from earthquakes may all have varying degrees of impact across different atmospheric parameters, thereby influencing the ionosphere. Additionally, a certain coupling relationship exists in different propagation paths, resulting in a multi-path coupling mechanism that further complicates the impact of earthquakes on the ionosphere. [PERSON] et al. [11; 12] pointed out that the release of radon gas and the propagation of acoustic waves through the chemical pathway can couple to form abnormal electric fields, which, in turn, couples with the ionosphere to produce abnormal disturbances. In the chemical pathway, the main factors influencing the lithosphere and near-surface atmosphere are radon gas and changes in the atmospheric electric field. Previous studies have suggested that there is a potential correlation involving heightened radon gas emissions, anomalies in atmospheric electric fields, and the incidence of earthquakes [57; 58]. Therefore, the data of radon gas and the atmospheric electric field were also collected, and we sought to explore the linkage between them and the extracted ionospheric TEC disturbance. The atmospheric electric field data of Pixian station (103.9\({}^{\circ}\)E, 30.9\({}^{\circ}\)N) near the epicenter were collected from the Data Center for Meridian Space Weather Monitoring Project ([[https://data.meridianproject.ac.cn/](https://data.meridianproject.ac.cn/)]([https://data.meridianproject.ac.cn/](https://data.meridianproject.ac.cn/)), accessed on 15 September 2023), and the radon gas data of Songpan station (103.6\({}^{\circ}\)E, 32.7\({}^{\circ}\)N) were obtained from the China Earthquake Networks Center. The time series curve of the two parameters before the Juzhaigou earthquake are shown in Figure 6.  
In order to observe the changes in radon gas, the study time range was extended sufficiently forward to observe the normal state before the accidental increase in radon gas. From 19 July to 25 July, the radon gas concentration rose, exhibited a fluctuating increase, and subsequently displayed a significant decline in the form of fluctuation, reaching its peak on 21 July. The radon gas concentration was relatively stable throughout other  
Figure 6: The variation of radon gas, atmospheric electric field, and Kp from 16 July to 8 August 2017. (When the datum is below \(-1\) kV/m and lasts for more than 2 h, it is displayed as a red curve in the temporal variation graph of the atmospheric electric field; in the panel of Kp, the red bar denotes indices greater than 3). instances; only a slight increase was observed on 28 July. Many studies have observed that radon gas, mainly in the three weeks before an earthquake, will rise remarkably [59; 60; 61; 62; 63]. [PERSON] et al. [58] and [PERSON] et al. [64] considered that the release of radon gas has a short- to medium-term impact on the ionosphere. Therefore, it is plausible to conclude that the abnormal increase in radon in Figure 6 may be related to the Jiuzhaigou earthquake. Significant fluctuations in the atmospheric electric field were observed during three periods: 16 July, from 20-28 July, and from 4-7 August. Referring to the Kp index, it can be seen that the fluctuation changes in the atmospheric electric field are more concentrated in the range of a Kp index greater than 3. [PERSON] et al. [65] researched the changing characteristics of the atmospheric electric field during 14 magnetic storms based on observation data from mid-latitude stations.