Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

L.A. Dremukhina at al. It has been established that classification of magnetic storm intensity according to Kp don’t ever coincide with that according to Dst. Among specified storms we have found 15 storms without Bz-events including 7 storms with -79 nT < Dst < -50 nT. The rest storms were weak (Dst > -50 nT, Ap < 20). All intense and major storms were accompanied by intense and durational Bz-events. Our statistical results support to known fact that not all CMEs originate a magnetic strom. At the same time they don’t support opinion of some researchers tha during the solar maximum CMEs don’t lead to occurrences of major magnetic storms as they don’t contain durational negative Bz-events. Occurrences o f major magnetic storms trends to increase with increasing product of Bz, x and V. But it should be impossible to evaluate intensity of a storm at Bz- event rather reliably. Note that three major magnetic storms in October, 2000, were caused by the most intense Bz-events (Bz >10 nT) with duration o f 18, 20, 25 hours correspondingly. Full halo, located near the vertical current layer under the bipolar coronal streamer belt over the solar region between coronal holes having opposite magnetic polarity, are considered to be a likely cause of major magnetic storms. However, hypothesis that theses solar regions are acceptable for IMF southward removal should be subject of special study. Conclusions We have been analysed specified negative and positive Bz-events, having |Bzl > 5 and duration x > 4 hours, basing on using statistics of 1967- 1984 and 1996 - 2004. During these two periods o f the study maximum number of occurrence of Bz-events was increased with increasing the solar activity when there were maximums of the solar spots and flares. During 1967 - 1984 Bz-events were accomplished by increasing IMF parameters (the solar wind velocity and density, IMF Bz component and plasma temperature) that is typical for regions o f interaction between high speed solar streams and the quiet solar wind. Increasing IMF parameters are caused by dominance of short time Bz-events in the regions of interaction between high and slow solar streams. Number o f Bz-events correlates with number of solar ejecta, especially with number o f events when the solar mass ejection reaches the Earth. But not all CMEs reached the Earth cause a magnetic storm. Eqcinoctial maximums o f Bz-events are observed under sunward IMF sector structure in spring and under anti- sunward one in autumn. Intense Bz-events caused by CME are observed in the solar activity maximum of 2000, and it isn’t agree with hypothesis according to which in the solar activity maximums there are no intense and durational Bz-events. Weak magnetic storms could develop without of occurrences of Bz-events in the solar wind. Intense and major storms are accomplished by intense and durational Bz-events. But it is impossible to evaluate intensity of a magnetic storm with estimating the intensity and duration of Bz-events. A c know ledgm en ts. This study is supported by RFBR grants 08-05-00896, 09-05-00495. References Gonzalez W.D., Joselyn J.A., Kamide, Y. H., Kroehl, G. Rostoker, B. Tsurutani, and V. Vasyliunas, What is a geomagnetic storm?, J. Geophys. Res., ,99(A4), 5771 - 5792 ,1994. Russell, С. T. and R. L. McPherron, Semi-annual variation of geomagnetic activity, J. Geophys. Res., 78, 92-100, 1973. Tsurutani B.T., Gonzalez W.D., Tang F., S. Akasofu, and E. Smith, Origin o f interplanetary southward magnetic fields response for major magnetic storms near solar maximum (1978-1979), J. Geophys. Res., A8, 8519 - 8531, 1988. 58