Variations in Schumann resonances and their relation to atmospheric electric parameters at Nagycenk station
Abstract. The present study is based on simultaneous measurements of the atmospheric electric potential gradient (PG) and Schumann resonances at Nagycenk station (Hungary) from 1993 to 1996. Annual and semi-annual variations detected previously in the relative amplitudes of Schumann resonances (SR) in the first three modes are confirmed by the extended data series applied here. The regular annual variation found in the PG (with winter maximum and summer minimum) is in the opposite phase, compared to that of the SR amplitudes. Nevertheless, even the PG (being a parameter of the DC global circuit) occasionally shows a distinct secondary peak in summer as indicated by the results of the present analysis (and corresponding to a recent study on further parameters of the DC global circuit). In spite of the presumed dominance of local influence over the global one, a suitable PG parameter correlates well with SR (representing the AC global circuit) on the annual time scale. It also became evident that a semi-annual variation (with spring and autumn maxima and winter and summer minima) is generally present in SR. Certain signatures of a semi-annual variation have also been revealed in the PG, however, the phase of this semi-annual variation does not fit the pattern shown by SR (and tropical surface air temperature, respectively). The representativeness of the PG data has also been checked by means of a single day's diurnal variations displaying a phase corresponding to that of the `Carnegie Curve'. Additionally, the coincidence of short-term changes (lasting some hours) both in the SR and the PG parameter is also demonstrated on a day disturbed by local factors. The results are discussed in the context of correlations between surface air temperature and parameters of the atmospheric electric global circuit shown by previous studies.