Rajesh Tyagi, Birbal Singh, O.P. Singh, R L Dua
Schumann resonance (SR) data obtained by employing a set of 3-component search coil magnetometer at tropical station Agra (geographic lat.27.2oN, long.78oE) are analysed for a period of 12 months between 01 April, 2007 and 31 March, 2008. By giving special attention to the study of first mode SR frequency corresponding to Xcomponent (north-south), various properties of global thunderstorm activities are deduced and interpreted. We show that global thunderstorm activities are concentrated in summer months with peak activity in July, 2007. This result is correlated with optical transient detector (OTD) data and a cross-correlation coefficient of 0.81 is found. The peak activity occurring in the month of July, 2007 is supported by a study of monthly variation of frequency range dF (dF=fn max-fn min) which shows a significant drop in the month of July. We further show that the general decrease in the first mode SR frequency observed at Agra and other Indian stations is due to minimum solar cycle period of 2008-09 (now increasing).
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