Spectrum of the
Earth-ionosphere cavity resonances
Average amplitude spectra from 2 to 100 Hz
for Arrival Heights, Antarctica (AH),
Sondrestromfjord, Greenland (SS),
and Stanford, California (SU) for the interval
January to March 1990.
The spectrums are dominated by sharp spectral features of the power
supply networks at 50 and 60 Hz. At the Stanford site, modulation
frequencies at 30 and 90 Hz occur, which result from
non-linearities of the power transmission system. Every spectrum exhibits
a carrier frequency of 82 Hz with a modulation of 0.2 Hz
that is produced by a Russian submarine communication system.
A variety of other spectral peaks of unknown origin occur occasionally
and distort the frequency range under consideration. Superimposed on
the 1/f natural background,
eight
Earth-ionosphere cavity resonances
can be
distinguished.
