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.

E.A. Revunova at al. 3. Analysis of influence of magnetic cloud parameters on its geoeffectiveness IMF Bz component has difficult distribution inside cloud. Its distribution depends on cloud configuration, i.e. on its parameters. It means that Dst-variation of geomagnetic disturbances, caused by interaction o f cloud with Earth s magnetic field, depends on cloud parameters. On the basis of statistical relationship of amplitude Bz magnetic field components and Dst-index, it is possible to establish values o f modeling cloud parameters responsible for generation of geomagnetic storm of the set intensity. Conformity of geomagnetic storm class on Dst-index to value IMF Bz components in Table 1 is resulted [Gonzalez et a l, 1994]. For performance o f analysis o f cloud parameters influence on its geoeffectiveness from base events by duration o f 25 hours, with radius 3 444 Re, average velocity 450 k m - c 1 and negative chirality have been selected. The selected magnetic clouds are large-scale and moving like to the Earth. Other could parameters changes according to ranges o f base modeling cloud parameters. T ablel. Conformity of geomagnetic storm class (Dst-index interval) to Bz component value o f IMF vector C lass sto rm D s t (m in ), n T B z (th re e h o u rs o n e n d ), n T W e a k - 3 0 - - 5 0 -5 M o d e ra te - 5 0 - - 1 0 0 -1 0 S tro n g - 1 0 0 - - 2 0 0 -1 5 E x tre m e -2 0 0 - -3 5 0 -3 0 The establishment ranges o f cloud parameters, corresponding to concrete geomagnetic storms class, under analysis magnetic field Bz component according to classification in Table 1 has been carried out. It was found, that the greatest number of cloud parameter combinations (43% from total numbers) can to cause strong magnetic storms that corresponds to result [Zhang et a l, 2004]. Moderate storms (22%) and weak storms (24%) are caused by approximately equal number o f magnetic cloud parameter combinations. Extreme storms can be caused only 11% of cloud parameter combinations. Further the detailed analysis o f each modeling magnetic cloud parameters has been carried out. In result ranges o f their values bringing the greatest contribution to geoeffective properties o f cloud have been established. In Table 2 percentage ratio o f modeling magnetic cloud configurations causing concrete geomagnetic storm class from the general numbers o f considered clouds is submitted. Table2. Value ranges of modelmg magnetic cloud parameters and classes o f magnetic storms which they can cause Ranges of change s Weak storms Moderate storms Strong storms Extreme storms ± (-1 0 -3 0 ) 7 7 % 5 0 % 4 4 % - ± (3 0 -7 0 ) 2 2 % 3 4 % 3 9 % 5 5 % ± (7 0 -9 0 ) 1% 18% 1 7 % 4 5 % Ranges o f change /1 ± (-1 0 -1 0 ) 13% 1 5% 1 2 % 1 7 % ± (1 0 -3 0 ) 2 1 % 19% 1 6 % 1 7% ± (3 0 -5 0 ) 23 2 1 % 2 1 % 1 9 % ± (5 0 -7 0 ) 2 1 % 2 3 % 2 5 % 2 2 % ± (7 0 -9 0 ) 2 2 % 2 2 % 2 6 % 2 5 % Ranges o f change Bo -4 4 - -3 6 2 .8 % 3 % 2 0 % 9 5 .1 % -3 6 - -2 4 .6 % 6 .1 % 3 7 .4 % 7 .9 % - 2 6 - - 1 8 1 9 .4% 2 2 .9 % 2 8 .5 % - -1 8 - - 8 3 6 .8 % 4 2 % - _ - 8 - 1 - - - _ 1 - 9 - - - _ 9 - 1 9 17% - - - 1 9 - 2 6 1 2 .8% 1 2 .2% - _ 2 6 - 3 7 4 .9 % 1 1 .1 % 5 % _ 3 7 - 4 5 1 .7% 2 .7 % 9 .1 % - 4. Technique of short-term forecast of geomagnetic storms intensity caused by magnetic clouds The technique of short-term forecast of geomagnetic storm intensity caused by magnetic clouds includes two basic stages. At the first stage establishment of cloud parameters on initial measurements magnetic field components and solar wind parameters on spacecraft is carried out. The description and testing this process is submitted in [Barkhatov et a l, 2010]. On the received parameters restoration o f full magnetic field structure in cloud is carried out. At the second stage the analysis of restored dynamics geoeffective Bz component in cloud is made. Further on the basis of Table 1 it is judged intensity of expected magnetic storm. The similar analysis for 27 CMEs registered on spacecraft ACE from 1998 to 2001 and established at the literature as magnetic clouds [Lynch et al ’ 2003] has been carried out. For example we consider in detail three magnetic clouds. Data from ACE for IMF components and 92