Novel analysis of a sudden ionospheric disturbance using Schumann resonance measurements

A spherical cavity between Earth and the lower ionosphere forms a global resonator for Extremely Low Frequency electromagnetic waves. Constant thunderstorm activity leads to the formation of a resonance field in the cavity, known as the Schumann resonance. Solar flare generated Sudden Ionospheric Disturbances (SID) modify the ionosphere affecting the ground-based radio communication systems. They are also expected to modify radiowave propagation in the cavity. In this paper, the Schumann Resonance spectral decomposition method is used for the first time to study the cavity resonance frequencies during the SID accompanying a strong X2.1 solar flare. We analyzed rapid changes in the frequencies and Q factors of the first five resonance modes using a 5 min timescale. The observed frequency shifts were compared to the ionizing solar flare fluxes in the UV, X-ray, and high-energy gamma rays.