Research on the Impact of Differences in Solar Flare Backgrounds of the Same-Class on Low-Frequency Time Code Time Service Signal

This study systematically investigates the impact of solar flares on the strength and timing deviation of China's low-frequency time code (BPC) time service signals under different occurrence background conditions based on same-class M1.1-class solar flare event. Seven representative observation cases were selected for the study, with calm day data 2–4 days before and after the cases used for comparison. The duration of solar flares and whether they were accompanied by geomagnetic storms were studied as variables. The study also conducted an in-depth analysis of the changes in BPC during solar flare occurrences using the SYM-H index, Kp index, SuperMAG geomagnetic data, and X-ray flux records from the GOES-16 satellite. The results show that when the X-ray flux reaches its peak, the BPC signals exhibit a sharp decay in strength and fluctuations in timing deviation. The longer the duration of the flare, the greater the disturbance to the signal. In the daytime mid-period, the response of BPC signals in the mid-to-low latitudes to geomagnetic storm background is not significant, as the dominant effect of solar radiation on exciting the D layer of the ionosphere masks the influence of geomagnetic disturbances. This study not only reveals the impact of background differences of same-class solar flares on BPC time service signals and provides strong support for the current understanding of signal-atmosphere interactions but also offers a theoretical basis for the anti-interference design of BPC systems.