Effects of a series of large flares from a sunspot group eruption on VLF propagation

The sunspot group continues to evolve, causing flares to erupt under the action of the atmospheric magnetic field. After the flare erupts, the ejected X-rays cause the electron concentration in the ionosphere to increase, and the equivalent reflection height of the ionosphere decreases. We investigate the correlation between the series of flares erupted by sunspot groups and the propagation of VLF signals. We used NOAA sunspot activity area data and solar flare data released by GOSE satellite, counted the series of flares erupted by sunspot group in 2000, and analyzed the size of the flare. Among them, the sunspot group numbered AR9077 erupted continuously with 15 M-level and above flares, X Level 3 flares. Received data from the Alpha VLF navigation station in Haikou, and observed a series of large flares erupted by AR9077. After the flare disk erupted, the phase anomaly of the VLF signal in the ground-ionosphere was caused. Analyze the flare according to the phase anomaly change, calculate the phase velocity when the flare occurs, the equivalent reflection height change, and the X-ray flux to predict the size of the flare. The calculations are consistent with the comparison of data published by the GOSE satellite. The observations show that the VLF signal correlates well with solar flares and sunspots. The VLF signal can be used as a reliable solution for predicting sunspots and solar flares, avoiding the impact of continuous flares of sunspots.