Lower ionosphere monitoring using magnetotelluric data

This study aims to investigate the relationship between Schumann Resonance (SR) characteristics and the D-region ionospheric electron density variations. In particular, it utilizes Magnetotelluric (MT) measurements as a complementary approach to estimate electron density profiles. By analyzing temporal variations in Schumann resonance frequencies, the work seeks to establish SR observations as a diagnostic tool for monitoring ionospheric electron density fluctuations. Magnetotelluric data comprising horizontal electric and magnetic field components (Ex, Ey, Hx, and Hy) are collected from the Mahanadi shear zone of the Odisha region in India. A frequency resolution of 0.016 Hz is achieved by averaging the Fast Fourier Transform power spectra of 64 data segments, sampled at 64 Hz. Frequency variation of the first three SR modes is revealed with maximum variations of 0.38, 0.13, and 0.37 Hz, respectively. During analysis, spectra show amplitude variations, particularly influenced by day-night transitions and terminator effects. Different Schumann resonance modes display phase shifts and varying levels of attenuation. The theoretical model has been elaborated, which couples the ionospheric electron density of the upper boundary of the ground-ionosphere waveguide with the ground MT data. Electron density is calculated over a period of 8 h. (9:00 a.m–4:00 p.m, IST) and compared with the FIRI model of the lower ionosphere.