Analysis of the low frequency fluctuations of the magnetic and electric fields prior to a strong earthquake of magnitude 8.0 on 12 May 2008 in Sichuan Province is given. We analyse the disturbances of the ionospheric electromagnetic field prior to the earthquake starting 2 weeks before this event, but detailed analysis is given for 6 and 9 May, 6 and 3 days prior to the earthquake, when the observed effects were strongest. Special attention is given to the characteristics of the spectra of these variations and the search for nonlinear effects. This analysis is possible in the time intervals when the extra low frequency (ELF) waveform was transmitted. Although the mechanism of energy transmission from the earthquake preparation zone to the ionosphere is not determined, it can be said that the ionospheric plasma is an unstable medium and that even a small perturbation can lead to variations in the electromagnetic field and plasma parameters. Some attempts at this discussion are given in the paper. The observations by Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) and discussed in this paper suggest the presence of plasma turbulence over the area above the Wenchuan Earthquake on 12 May 2008. The characteristics of the observed disturbances are studied with wavelet and bispectral analysis, tools which are more relevant for analysing plasma turbulence.

We report the observation of ELF and VLF signature of sprites recorded on the low altitude satellite DEMETER during thunderstorm activity. At an altitude of ~700 km, waves observed on the E-field spectrograms at mid-to-low latitudes during night time are mainly dominated by up-going 0+ whistlers. During the night of 20 July 2007 two sprites have been observed around 20:10:08 UT from the observatory located on the top of the mountain Śnieżka in Poland (50°44'09" N, 15°44'21" E, 1603 m) and, ELF and VLF data have been recorded by the satellite at about 1200 km from the region of thunderstorm activity. During this event, the DEMETER instruments were switched in the burst mode and it was possible to register the wave forms. It is shown that the two sprites have been triggered by two intense +CG lightning strokes (100 kA) occurring during the same millisecond but not at the same location. Despite the distance DEMETER has recorded at the same time intense and unusual ELF and VLF emissions. It is shown that the whistler wave propagates from the thunderstorm regions in the Earth-ionosphere guide and enters in the ionosphere below the satellite. They last several tens of milliseconds and the intensity of the ELF waveform is close to 1 mV/m. A particularly intense proton whistler is also associated with these emissions.