Parameters of global thunderstorm activity are deduced from long-term frequency amplitude records of the first three Schumann resonance (SR) modes performed at the Nagycenk Observatory (47.6°N, 16.7°E), Hungary, from May 1993 to May 1996. The variations of the daily frequency range of each mode, which are characteristic of the changes of the effective source width, exhibit annual and semiannual variations. Annual and semiannual variations are present in both the recorded data and the parameters of global thunderstorm activity. The effective source width varies over 3-4 h at solstices to 5-6 h during the equinox conditions. A period of about four months also appeared in the spectra of the recorded data. A similarity was found between the patterns of the annual and semiannual variations of the daily frequency range, and the changes in median solar time, apart from a three-month phase lead of the astronomical data. The similarity might be due to an unknown solar-terrestrial link. Two approaches were used for the parameterisation of the global thunderstorm activity. One of these employs the preliminary evaluation of the source-observer distance (SOD) using the ratio of individual mode amplitudes. Variations of the source intensity are obtained after dividing the amplitude recorded by that calculated for the established SOD. The second approach applies a direct summation of the individual mode intensities. Numerical simulations showed that such cumulative intensity depends on the level of the global thunderstorms rather than on the SOD. The two estimates were compared and the conclusion was made that these coincide to within ±30%. The maximum of the global thunderstorm activity occurs in summer, in the Northern hemisphere, and the minimum is observed in winter with a two-fold characteristic variance.
|Number of pages||13|
|Journal||Journal of Atmospheric and Solar-Terrestrial Physics|
|Publication status||Published - Feb 1998|
ASJC Scopus subject areas
- Atmospheric Science
- Space and Planetary Science