Abstract:
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 (70.8S,
11.7E), served to examine the SR parameters, namely
the amplitude and frequency, in the north-south (HNS)
and east-west (HEW) 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.
