## 4 The 8 January 2022 Menyuan \(M_{\rm S}\) 6.9 EQ  
Figures 8 and 9 display, respectively, the weekly ionic and electronic variations at nighttime on the Chinese mainland during the Menyuan \(M_{\rm S}\) 6.9 EQ on 8 January 2022. Parts of the data on 20-21, 27 December 2021, 1, 3 and 9 January 2022 were eliminated when the data were processed weekly at that time, due to a daily Kp index above 3 or an hourly Kp index 4, as noted in Figure 6b. In northern China, variations in ion density on 14-20 December 2021, shown in Figure 8a, and variations in ion density and electron density, shown in Figures 8b and 9b, during the next week were obvious. However, there were no corresponding changes for electron density during 14-20 December, and these fluctuations were located in the northeast of China, where there are relatively high background values for these two parameters, as mentioned above. Thus, these irregularities were thought to be less reliable when the data were processed at that time. Additionally, there were no obvious variations in the range of the Chinese mainland during 4-10 January 2002, when the Menyuan \(M_{\rm S}\) 6.9 EQ took place. The ionospheric variations, which attracted our attention, were those that occurred during 28 December 2021-3 January 2022, when the related data were processed on 5 January 2022 (the real data have a two-day delay). Figures 8b and 9b show this anomalous condition occurred in ion density and electron density, respectively. Figure 7: Fluctuations of (**a**) He\({}^{+}\) and O\({}^{+}\) densities and (**b**) electron density registered by the CSES satellite on 8 May 2021, 14 days before the Maduo \(M_{\rm S}\) 7.4 EQ. Obvious variations associated with this Maduo event are labeled with black arrows. In order to confirm the reliability of these anomalies, we firstly examined the related orbits passing through the anomalous area and then specified the right orbit where the anomaly appeared. Figures 10 and 11 show, respectively, the variations in the ionospheric parameters of (a) He\({}^{+}\) and O\({}^{+}\) and (b) Ne in the specified orbit of 21668_1 on 28 December 2021 and its revisiting orbit 21744_1 on 2 January 2022. The ionospheric anomaly took place at about 19:00 in these two days. Secondly, we also reexamined the  
Figure 8: Variations in O\({}^{+}\) density during the periods of (a) 14–20 December 2021 (b) 21–27 December 2021, (c) 28 December 2021–3 January 2022, and (d) 4–10 January 2022. The Menyuan \(M_{\rm S}\) 6.9 EQ is labeled with a red dot (and with a black circle in the third panel). Figure 9: Variations in electron density during the periods of (a) 14–20 December 2021 (b) 21–27 December 2021, (c) 28 December 2021–3 January 2022, and (d) 4–10 January 2022. The Menyuan \(M_{\rm S}\) 6.9 EQ is labeled with a red dot (and with a black circle in the third panel). corresponding Kp index on 28 December and found that the hourly Kp values at 18:00 and 21:00 were 1 and 0, and the Kp values of the same time period on 2 January 2022 were 2 and 3. In view of this, the variations recorded this time, within the Chinese mainland were of high reliability as EQ precursors. So, we reported this anomaly and gave a warning of an impending EQ around the ionospheric anomalous area within two weeks, when a usual weekly meeting was held on 7 January 2022. The second day after the warning was given, a large EQ with a magnitude \(M_{\rm S}\) 6.9 occurred on 8 January 2022 in Menyuan area, Qinghai province, with an epicenter located at 37.77\({}^{\circ}\) N and 101.26\({}^{\circ}\) E and a depth of 10 km. This event occurred 11 days and 6 days after the appearance of the corresponding abnormalities, and it was located almost at the area where the obvious ionospheric disturbances occurred (see Figures 8b and 9b).