JJI甚低频台站信号对太阳耀斑事件的响应特性

The increase in X-ray flux during solar flares affects the electron density in the Earth's ionosphere and thus changes the waveguide state, leading to the disturbance in signals observed by the VLF receiver. During the solar flares that occurred on 8 September 2017, both the VLF receiver at Wuhan and Suizhou in Hubei Province detected abnormal signal perturbations at 22.2 kHz from the JJI transmitter (130°49'E, 32°04'N) in Japan. The observations show that the amplitude of the received JJI signal has different responses to different solar flares. Interestingly, we also found that the response types of the two receivers at Wuhan and Suizhou are significantly different for the same solar flare. Based on the observations of Wuhan and Suizhou receivers during 2017-2019, the statistical analysis of signal amplitude disturbance events from JJI station related to solar flares is performed. The results reveal that the response types in both paths are related to flare intensity and the occurrence time. Four different types of response are investigated, namely, twice rising and falling, first rising and then falling, falling and rising. However, the proportion of the four response types are different. The fitting results also show that the disturbed amplitude of the signal is positively correlated with the integration of X-ray flux, while the linear fitting slope of the two paths is different. The JJI signals received at Wuhan and Suizhou both belong to the short-distance transmission along the latitude direction, and the two receiving stations are close to each other. Thus, the two propagation paths are quite close. These results for the responses of the JJI signal to solar flares in the two paths are helpful to understand the propagation of VLF signals and shed light on monitoring solar activities by VLF signals.