1. Centre for Fusion, Space and Astrophysics, Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom;
2. School of Space Research, Kyung Hee University, Yongin, 446-701, Korea
3. St. Petersburg Branch, Special Astrophysical Observatory, Russian Academy of Sciences, 196140 St. Petersburg, Russia
4. Institute of Solar-Terrestrial Physics, Siberian Branch of Russian Academy of Sciences, Irkutsk 664033, Russia