Schumann Resonances Observed at Maitri, Antarctica:Diurnal Variation and its Interpretation in Terms of Global Thunderstorm Activity

Schumann resonances (SRs) are the AC components of the global electric circuit and are excited by the lightning activity within the Earth-ionosphere waveguide. An induction magnetometer, which was operated from the Indian Antarctic station, Maitri (70.8°S, 11.7°E), served to examine the SR parameters, namely the amplitude and frequency, in the north-south (H_NS) and east-west (H_EW) magnetic components. The analysis for the first resonant mode presented in this work reveals a strong UT variation in its amplitude in seasonal as well as yearly timescales. The NS amplitude reveals a semi-diurnal variation with peaks at ~1000 and ~2100 UT, whereas the EW amplitude exhibits a strong diurnal variation with a pronounced peak at 1600 UT. The diurnal curves for the frequency for both components are similar in nature to those for the amplitude, but for a time shift. The diurnal trend in the amplitude is retained irrespective of seasons, whereas significant difference are noticed in the frequency behaviour between the summer and winter seasons, especially in the EW component. The observed diurnal variation in the SR intensity is explained in terms of the dominant thunderstorm activity centred over the three convectively active regions: Asia/Maritime Continent (Indonesia), South America and Africa. The diurnal variation in frequency depends not only on the location of the thunderstorm region with respect to the observer, but also on the ionospheric day/night conditions and the Earth-ionosphere cavity thickness.