Gabriella Sátori

Parameters of global thunderstorm activity deduced from the long-term Schumann resonance records

Abstract Parameters of global thunderstorm activity are deduced from long-term frequency and amplitude records of the first three Schumann resonance (SR) modes performed at the Nagycennk 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.

Spectral characteristics of Schumann resonances observed in central Europe

The vertical electric field component in the frequency range of Schumann resonances has regularly been measured at the Nagycenk Observatory in Hungary, in Central Europe since May 1993. The actual peak frequencies and the amplitudes belonging to them are determined for the first three modes. Each mode has its own character and they show distinct daily and seasonal variations. The recurrence tendency of these variations from year to year is also presented. The significant annual and semiannual variations of the amplitudes support the suggestion that the Schumann resonance as a global phenomenon is sensitive to small temperature variations in the tropical atmosphere.

El Niňo related meridional oscillation of global lightning activity

The self-consistent behavior of the frequency level and semiannual intensity variations of the first three Schumann resonance (SR) modes observed at Nagycenk (47.6°N, 16.7°E) indicates a southward shift in the global position of the lightning activity in warm El Niňo years and a northward shift in cool La Niňa years, especially in the longitudinal range where Africa dominates the activity. The third SR mode has a crucial role in recognizing these meridional shifts due to the special angular distance of Nagycenk with respect to the African thunderstorm region. The diurnal zonal redistribution of the worldwide thunderstorm activity manifests in characteristic daily frequency patterns. The preserved daily frequency patterns with changing frequency levels in the same months of the different years imply that the meridional shifts of the lightning activity exist in worldwide sense on the ENSO time scale. The estimated shifts are about 4–8° in latitude.

Monitoring Schumann resonances—I. Methodology

Abstract The complex demodulation as a spectral technique has been used for the quasi-continuous determination of the actual frequencies of Schumann resonances. Applying this method, the first three modes of the vertical electric component have been measured regularly in the Nagycenk Observatory (47.6°N, 16.7°E) since May 1993.

Monitoring schumann resonances-11. Daily and seasonal frequency variations

Abstract The time variations of the Schumann resonance peak frequencies for the first three modes are presented in the vertical electric component measured in the Nagycenk Observatory (47.6°N, 16.7°E) from May 1993 to August 1994. The average daily frequency patterns are different for the three modes, and each mode shows a distinct seasonal variation. The recurrence of this seasonal variation is also shown. The daily frequency range, in which the frequencies shift, is wider in winter than in summer in all three modes. The mean frequency level also shows a seasonal variation in the third mode. A spring-autumn asymmetry has been found in case of the first mode.

Schumann Resonance Signatures of Global Lightning Activity

This chapter is concerned with the Earth’s Schumann resonances (SR) and their application to understanding global lightning. The natural electromagnetic waves in the SR frequency range (5 Hz to approx. 60 Hz) radiated by lightning discharges are contained by the Earth-ionosphere cavity. This cavity excitation by lightning can occur as a single energetic flash (a ‘Q-burst’), or as an integration of a large number of less energetic flashes (the ‘background’ resonances). In principle, continuous observations of SR parameters (modal amplitudes, frequencies, and quality factors) provide invaluable information for monitoring the worldwide lightning activity from a single SR station. Relationships between the variation of SR intensity and global lightning activity are shown. Connections between the change of diurnal modal SR frequency range and the areal variation of worldwide lightning are demonstrated. The temporal variation of the diurnal SR frequency patterns characteristic of the global lightning dynamics is also presented. Distortions of ELF waves propagating between the lightning sources and the observer are theoretically discussed based on the TDTE (two-dimensional telegraph equation) technique, focusing on the role of the day-night asymmetry of the Earth-ionosphere cavity. Theoretical and observational results are compared. Both instruments for SR observations and spectral methods for deducing SR parameters are reviewed. Experimental findings by SR on global lightning variations on different time scales (diurnal, seasonal, intraseasonal, annual, semiannual, interannual, 5-day, long-term) are summarized. The growing use of SR measurements as a natural diagnostic for global climate change is emphasized.

Combined ionospheric effect due to Forbush decreases and magnetospheric high energy particles at mid-latitudes

Abstract After geoactive solar flares the Forbush decrease of galactic cosmic rays and magnetospheric high energy particles can cause opposite ionization effects in the ionospheric D -region at mid-latitudes. This has been shown by the change of the ELF and VLF atmospheric radio noise level and that of the LF absorption. The frequency dependence of these variations has been interpreted by waveguide mode theory and full-wave solutions using D -region electron density profiles under conditions characteristic of these ionization disturbances.

Anomalous behavior of Schumann resonances during the transition between 1995 and 1996

Anomalous behavior of Schumann resonance (SR) parameters is presented in interannual relations for the first time. The mean daily intensity of the first three SR modes measured in the vertical electric component at the Nagycenk Observatory (47.6°N, 16.7°E), Central Europe, was significantly higher in December 1995 and January 1996 than in the same months 1 year before. The largest relative SR intensity deviations occurred in the third part of December 1995 and in the evening hours (2000-2200 UT), when the lightning activity of the South American thunderstorm region is the most intense. In January 1996 the largest relative SR intensity deviations appeared in the early morning hours (0000-0030 UT), when the worldwide thunderstorm activity is at a minimum. This result suggests that a lightning activity in the Pacific region was not as sparse in January 1996 as it was in January 1995. The time variation of the maxima of the SR intensity ratios indicates a westward propagation with trade wind speeds of about 2 to 8 m s -1 from the end of December 1995 about to the end of January 1996. The anomalous SR intensity in December 1995 is attributed to a small increase in the surface air temperature (about 0.2°C) and to the extension of the thunderstorm region indicated by the SR frequency range variation. It is also suggested that this warmer air mass was advected by easterlies from the end of December 1995 over the cooler Pacific in January 1996 causing more intense lightning activity there.

Observation of TLES in central europe from hungary supported by LINET

More than one hundred different transient luminous events (TLEs) i.e. sprites, sprite halos and one blue jet‐like emission have been observed in Central Europe at a new optical observation site in Sopron, Hungary, during the summer of 2007. The recently developed LINET lightning location network supplied information about the lightning activity in the region. This was the first time that data from this network was used to support TLE observations and to help interpret the results. TLE‐triggering lightning flashes were identified by their radiation in the ELF (Extremely Low Frequency) band, appearing as coherent transient signals with enhanced amplitudes in the monitored field components of the atmospheric electromagnetic field at NCK station in Hungary. Individual lightning flashes could be associated with 92% of the optically observed events. No ELF transient could be associated with the blue jet‐like emission, and for one sprite neither a corresponding transient nor any causative lightning flash could b...

Effects of Energetic Solar Emissions on the Earth–Ionosphere Cavity of Schumann Resonances

Schumann resonances (SR) are the electromagnetic oscillations of the spherical cavity bounded by the electrically conductive Earth and the conductive but dissipative lower ionosphere (Schumann in Z Naturforsch A 7:6627–6628, 1952). Energetic emissions from the Sun can exert a varied influence on the various parameters of the Earth’s SR: modal frequencies, amplitudes and dissipation parameters. The SR response at multiple receiving stations is considered for two extraordinary solar events from Solar Cycle 23: the Bastille Day event (July 14, 2000) and the Halloween event (October/November 2003). Distinct differences are noted in the ionospheric depths of penetration for X-radiation and solar protons with correspondingly distinct signs of the frequency response. The preferential impact of the protons in the magnetically unshielded polar regions leads to a marked anisotropic frequency response in the two magnetic field components. The general immunity of SR amplitudes to these extreme external perturbations serves to remind us that the amplitude parameter is largely controlled by lightning activity within the Earth–ionosphere cavity.