Observations and Numerical Simulations of the Effects of the Gamma Ray Burst 221009A on the Lower Ionosphere

This paper investigates the impact of a powerful gamma ray burst (GRB) that occurred on 9 October 2022, on the Earth's environment using a very low frequency receiver (VLF) to probe the lower ionospheric region (the D region). In addition to the VLF data analysis, we employ numerical simulation through the Long Wavelength Propagation Capability code (LWPC) to derive the increase in the D− region electron density. Our results revealed discernible perturbations in amplitude and phase across all transmitter paths (NAA, DHO, ICV, and NSC) to the Algiers receiver persisting for 40 min. At the maximum of the signal perturbation, the LWPC simulation results showed a decrease in the mean new reference height h′ from 74 to 65.71 km, along with an increase in the sharpness factor β from 0.3 to 0.4875 km−1. Under these new conditions, the electron density increased from its ambient value (216.10 cm−3) to 33.7 103 cm−3. Plain Language Summary Gamma rays are good indicator of the activity that is taking place in the universe. As they travel freely in the space, these phenomena can cause strong disturbances in the Earth's environment. In 9 October 2022, a powerful burst of gamma rays was recorded by many satellites in the near Earth space. This radiation burst was responsible of the ionospheric disturbance resulting in a modification of the propagation conditions of the radio waves. The intensity of the disturbance as well as its spatial extent can be determined through the analysis of different radio signals propagation and the level of the ionization increases. These results give us insight about the coupling between the gamma rays and the ionized layer of the Earth atmosphere. Key Points The impact of GRB221009A on the VLF transmitter signal dynamics captured by measurements from the Algiers VLF receiver is reported A numerical simulation showcases the changes in electron density dynamics in the ionosphere's D‐region during the GRB221009A phenomenon The model accurately replicates the variations in VLF signal parameters (amplitude and phase) recorded during the GRB221009A event