Schumann resonance frequency variations during sudden ionospheric disturbances

Fluctuations of the fundamental and harmonic frequencies of the Schumann (earth-ionosphere cavity) resonances measured near Tromsø, Norway, on 28 March 1979 are examined on a timescale of ≲ 20 minutes. Their relationships with two sudden ionospheric disturbance events and one other geophysical event is investigated. The experimentally observed frequency variations are, in some cases, at variance with the theoretical predictions of Madden and Thompson (1965).