Evidence of CME‐Magnetospheric Shock Disturbance of the D‐Region Observed in the VLF Signal

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Abstract The observation of the D‐region response to the interplanetary shock (IS) during the storm of 17 March 2015 is carried out using two very low frequency (VLF) transmitter signals (NRK and GQD) recorded at Algiers and Tunis. Data from THEMIS‐E and RBSP are used to correlate between the ground and satellite observations. The important finding is the wavy structure of the perturbations observed on the two VLF signals tens of seconds after the space detection of the shock, in concordance with the RBSP electric field measurements. The measured VLF signal amplitude and phase perturbations were: −0.65 dB, 5.81° for NRK and −0.12 dB, −126° for GQD measured at Algiers. For Tunis receiver, the perturbations were: −0.58 dB, 4.7° for NRK and 0.15 dB, −1.19° for GQD. In addition to the observations, simulations of the NRK signal perturbations were done using the long wavelength propagating capability code to determine the electron density modification that lead to the measured perturbations. The simulation results showed that the modified Wait's parameters above the NRK transmitter were: 80.391 km for h′ and 0.43 km−1 for β in the case of NRK‐Tunis path. Concerning the NRK‐Algiers path, the simulation gave 80.316 km for h′ and 0.431 km−1 for β. From these parameters values, the modified electron density was not important to explain the observed perturbations. Therefore, the IS effect could be explained by induced heating of the ionosphere due to the penetration of the electric field which leads to the changes of the ionospheric conductivity.

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