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[1] The ELF measurements in Russian observatories Lovozero (the Kola Peninsula) and Lekhta (Karelija) during the solar proton event of 14 July 2000 show the decrease of frequencies of the first and second Schumann resonance modes of $0.4 Hz and the increase of the first-mode bandwidth from 0.8 to 1.5 Hz. The solar X-ray burst, preceding the proton precipitation, is accompanied by the increase of the first-mode frequency. Approximate formulas for frequencies and qualities of the two first modes are found for a two-layer model of the Schumann resonator (SR). The changes of the SR parameters are a response of the Earth-ionosphere resonator to large-scale disturbances of the polar ionosphere.

A new computer‐based ELF/VLF system for locating lightning discharges has been developed. Both the arrival azimuths of atmospherics and the distances to their sources are estimated. The direction‐finding technique uses the Poynting vector calculated directly in the time domain over the full band pass of the receiver. Both the distance of the lightning discharge and the ionospheric height can be estimated from the phase spectrum of the first‐order mode of the Earth‐ionosphere waveguide. The latter is approximated with a model function having the distance and the height as the main parameters. Two ways were applied to obtain the spectrum of the first mode: the radial component of the horizontal magnetic field was used, which contains only a minor component of the zeroth mode, or the mode decomposition problem was solved. The system has been used to locate lightning sources in Africa and Asia from a scientific vessel during its voyage in the Atlantic and Indian Oceans in 1991. The overall uncertainties are estimated to be a few degrees for the source bearing, 5% for distance, and 1% for the effective height of the ionosphere; yet these estimates need an additional confirmation by comparison with independent and more exact techniques.

[1] This paper deals with the computation of extremely low frequency propagation associated with the Schumann resonance phenomena and the reconstruction algorithm for source lightning location on the basis of measured Schumann resonance data. The finite difference equations are derived in terms of discretized magnetic fields in the spherical coordinates, introducing the azimuthal symmetry for simplicity. The most reliable electron and neutral density models in the atmosphere and the ionosphere can be used to describe extremely low frequency wave propagation. A linear inverse problem for the reconstruction is formulated using the computed spectra as a set of basis functions to identify lightning distributions with respect to the distances from any observatories to the global thunderstorm centers. Numerical experiments allow us to evaluate properties and precision of the solution in the absence or in the presence of noise in the initial spectral data. The inverse problem is applied to the experimental data collected at a field site in Japan, and distribution of global lightning activity is reconstructed for the data covering the period from March to December 1999. The reconstructed data show a reasonable set of distances from the observatory to well-known global thunderstorm centers, and they indicate the seasonal drift of lightning activity. The problems that were involved in solving the inverse problem are also discussed.

Abstract.Results of simultaneous LF subionospheric monitoring over two different propagation paths prior to the very strong Tokachi earthquake (near the east coast of Hokkaido Island, 25 September 2003) of magnitude 8.3 are presented firstly. Nighttime amplitude fluctuations of the Japanese Time Standard Transmitter (JG2AS, 40 kHz) signal received at Moshiri (Japan, 142 • E, 44 • N) and at PetropavlovskKamchatski (Russia, 158 • E, 53 • N) were analyzed. As a possible precursory signature we observed synchronous intensification of quasi periodical 16-day variations of the dispersion in the signals received at both observation stations before the earthquake. The strongest deviations observed as a rule were depletions of signal amplitude probably connected with increase of loss in the ionosphere by the enhancement of turbulence. This is due to dissipation of internal gravity waves (IGW) at the lower ionosphere heights. A scheme for seismo-IGW-planetary waves (PW) interconnection has been justified to explain the observed connection with strong earthquakes. It considers the seasonal variability in the signal.

Abstract. Surface Latent Heat Flux (SLHF) is an atmospheric parameter proportional to the evaporation from the Earth's surface. SLHF has been found to exhibit an anomalous behavior in the epicentral region prior to several coastal earthquakes. Sub-ionospheric low frequency (LF) radio sounding measurements have shown its potentiality for the short-term earthquake forecasting since the last decade. The anomalous SLHF and nighttime LF sub-ionospheric signals are found to show complementary nature associated with the large Tokachi-Oki earthquake of 25 September 2003. Such complementary nature of parameters may prove to be potential in providing early warning information about an impending earthquake.