Variations of the global lightning distribution revealed from three-station Schumann resonance measurements

Abstract

Schumann resonance (SR) observations performed simultaneously by a global network consisting of three stations (Lekhta (Karelia, Russia), Moshiri (Hokkaido, Japan), and West Greenwich (Rhode Island, United States)) during almost 1 year were used for mapping world thunderstorm activity. A two-stage inverse problem is solved for locating lightning sources distributed over the Earth's surface from the SR background signals. The first stage consists of inversions of the SR magnetic field power spectra to the distributions of lightning intensity by distance relative to an observation point. The obtained distance profiles of intensity of sources are used as tomographic projections for reconstructing a spatial distribution of sources in the second stage. We have suggested the use of source distance profiles obtained from the spectra of outputs of two orthogonal magnetic antennas operating at each observatory as separate tomographic projections. It is shown that the implementation of additional information on the azimuthal distribution of sources, provided by angular selectivity of magnetic sensors, significantly improves the quality of global lightning mapping under the condition of a limited number of observation stations. Maps of the global lightning distributions constructed by the result of inversions of SR spectra show that the most active regions vary zonally on the seasonal time scale and meridionally on the diurnal time scale being connected mainly with continental areas in the tropics. Copyright 2010 by the American Geophysical Union.