Physics of auroral phenomena : proceedings of the 34th Annual seminar, Apatity, 01 - 04 March, 2011 / [ed.: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 231 с. : ил.

V. V. Pchelkin, E.N. Yakushenkov For each measurement of the horizontal component of the magnetic inductance vector the arrival azimuth was calculated. The calculation results were presented in the form of daily distribution of azimuths. The number of signals that received in the corresponding range of angles and times was shown by color. This form is better for determining the activity of the thunderstorm centers (compared with the daily course of signal intensity). 3. Results and discussion 1) In the noise magnetic field in the frequency range near the first Schumann resonance (as it was supposed) we have detected clearly anisotropy. This fact is interpreted as a result of irregular spacing of thunderstorm activity on the Earth surface and its changers in the course of time. That leads to the occurrence of different dominant arrival directions of lightning signals during a day (see Fig. 1). (In a daily total distribution of azimuths the anisotropy of arrival directions of noise signals is revealed too - see Fig. 2). 2) We found that the dominant arrival directions of lightning signals have natural seasonal variation (Fig. 3), which is caused by the seasonal movements of the world thunderstorm centers. The calculations of the dominant arrival directions of lightning signals at different times showed that the average bearing of the Asian World Center varies about 25 degrees from winter to summer, the bearing of the African Centre remains practically unchanged, the bearing of the American center varies about 45 degrees (see Fig . 3). This agrees well with the meteorological information about the seasonal changes of location of the world thunderstorm centers (Christian et al., 2003). According to this information remarkable increasing of “American” direction activity and its change in depending on time (the time of maximum increases by 1,5-2 hours) can be explained by widening territory of thunderstorm activity towards North America in summer. But the change of location of African center consists of the “South-North” motion. It doesn’t result in changes of azimuth on source signals in the observation place (Fig 3). The territory of Asia thunderstorm activity widens in summer towards West, and it results in a change of “Asian” bearing about 25 degrees. 3) Activity of the thunderstorm centers increases in the summer period in a different degree in comparison with winter. The approximate estimates of the number of signals coming from different centers show that the activity of the Asian Centre increases more than the activity of African and American Centers. The method of the estimates was based on the approximate calculation of the number of signals within the boundaries of different bright spots, correlated with the activity of the world thunderstorm centers (see Fig. 3). Acknowledgements. Author would like to thank M.I. Beloglazov, A.N. Vasiliev, S.P. Noskov and A.I. Voronin for equipment preparation, and to the personnel of the Lovozero Observatory for the measuring control. This work was supported by the Fundamental Research Program of Department Physical Sciences of the Russian Academy of Sciences (project № 4.5 - Atmospheric electricity in the lower atmosphere of the polar latitudes). References Bliokh, P. V., Nikolaenko, A. P., and Filippov, Yu. F.: Schumann Resonances in the Earth-Ionosphere Cavity, Peter Perigrinus, London, 1980. Beloglazov, М. I., Akhmetov, О. I., Vasil’ev, A. N., and Kosolapenko V. 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