Quantyfing the global lightning activity in absolute unints using Schumann resonance spectral decomposition method and the data from the World ELF Radiolocation Array

Abstract:

The extremely low frequency (ELF) electromagnetic waves in the Earth-ionosphere cavity are generated mainly by lightning discharges, originating from the tropical thunderstorm centers. The Earth-ionosphere spherical cavity forms a global resonator for the ELF waves. In a spherical damped resonator, like the Earth-ionosphere cavity, the electromagnetic field is the superposition of the standing wave (resonance) field with the traveling waves field, which transfers the energy from lightning flashes to the global resonator. This component is quite strong close to the source and weakens with source-observer separation and is a major reason for an asymmetric shape of the observational Schumann resonance (SR) power spectra. In physics the process, where the resonant field interference with the background is very well known and in such a case the resonant lines are always asymmetric. However, it is possible to separate the resonance field component from the signal using the spectrum decomposition method proposed by Kułak et al. [2006].

Here, we examine the activity of African thunderstorm center using Schumann resonance data collected by the two ELF stations built under the World ELF Radiolocation Array (WERA) project. The first ELF station in located in Poland and it has been recording data continuously since the end of 2004. In May 2015, another ELF station was installed in the Hugo Wildlife Area in Colorado as part of our project WERA. We binned the ELF data in 10-minute files and we derived the SR power spectra. In the next step the decomposition curve, which describes 7 asymmetric SR modes was fitted to the observational data. Using the algorithm, described in Dyrda et al. [2014], we calculated the distances to the tropical thunderstorm center located in Africa with the spatial resolution of 0.1 Mm. This is done independently for each of the ELF stations from WERA array. Then using the information about the distances and about the size of our magnetic antennas beam we derived the possible locations of the storm center on the African continent and hence we construct the 2D thunderstorms activity maps. Moreover, we calculated the thunderstorm intensities in absolute units C² m² s^-1 and compared them with our previous findings [Dyrda et al., 2014].