Physics of auroral phenomena : proceedings of the 40th annual seminar, Apatity, 13-17 March, 2017 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2017. - 143 с. : ил., табл.

Possible cause o fsolar wind magnetic cloud shock waves result of a violation of the balance of pressures. In this study, the relationships of the total gas-kinetic and magnetic pressures (Fig. 2a), gas-kinetic and magnetic pressures separately (Figs. 2b, c), on «Solar wind-magnetic cloud» boundary are devoted. The dependence of the relative velocity of magnetic clouds on these two pressures (Fig. 2d, d) is devoted too. In all the diagrams in Fig. 2, the gray triangles correspond to magnetic clouds without shock waves, black circles to clouds with shock waves. According to Fig. 2a, for magnetic clouds without shock waves (gray triangles) there is balance of the total gas-kinetic and magnetic pressure on «Solar wind-magnetic cloud» boundary (they found along the line of equality of pressures). In the case of clouds with shock waves (black circles) there is a significant excess o f the total pressure at cloud body above the pressure in the Solar wind. Consequently, there is an expansion of magnetic clouds with shock waves, as a result of which their boundaries acquire an additional velocity. Investigation of the ratios of gas-kinetic and magnetic pressures in the Solar wind and in magnetic clouds (Figs. 2b, c) showed that the magnetic pressure in clouds with shock waves exceeds the corresponding values in Solar wind. This indicates the main contribution of magnetic pressure to the acceleration of the leading part of the cloud. Analysis of the dependence of cloud relative velocity on intra-magnetic and intra-gas-kinetic pressures also demonstrates the effect o f magnetic pressure on the acceleration of fast clouds (Fig. 2e, black circles). The gas-kinetic pressure in Solar wind and in magnetic clouds are an order of magnitude lower than the magnetic one and does not make a significant contribution to the acceleration of clouds. Л Л , C l u , a в-* , o,6 c_ £ m ra o< О с / О . * 5 М т 0.04 С ^ 4 ш С o j » . i_- а.02 Q- « / * , , с 'и .__ " " t m j w s , , . „-"Г" JF **J ‘ ’ Q. « i f f e * ---- £ 01 й £ * * Г * ‘ « ОМ 0.1 0,15 С-2 0 0.01 «02 0.03 Ш <3.05 ф.05 0 0.05 0 ! 015 0.2 Pm+PnkT, SW, nPa PnkT, SW, nPa Pm, SW, пРа 550 300 * 250 • 350 300 250 _<я 200 „ W 200 * , е 150Д. * Е v , tooД * 10 *•« ф . g) 20 ? • ? .* , ^ ° * * > 0 •50 -«О А * •too5" - 100 . •150 .150 0 0.05 0.1 0.15 0.2 о 0.1 0.2 0.3 0.4 0.5 0.4 PnkT, МО, nPa Pm, МО, пРа Figure 2 Thus, as a result of the research carried out, it is established that the main condition for the existence of shock waves in front o f magnetic clouds is that the velocity of the cloud exceeds the velocity o f Solar wind by more than 50 km/s. In this case, the relative velocity of the cloud turns out to be higher than the velocities of the sound waves and Alfven waves in Solar wind. It is shown that the acceleration and expansion of magnetic clouds occurs due to the excess o f the magnetic pressure in them above the corresponding pressure in the surrounding Solar wind. A cknow ledgm en ts. This work was supported by grant RFBR №16-05-00608 and State Task of Minobmauki RF № 5.5898.2017/8.9. References [1] Barkhatov N.A., Revunova E.A., Levitin A.E. Classification of space-weather complexes based on solar source type, characteristics of plasma flow, and geomagnetic perturbation induced by it // Geomagnetism and Aeronomy. T 54 № 2 P 173- 179. 2014. [2] Zhang J., Liemohn M.W., Kozyra J.U., Lynch B.J., Zurbuchen Т.Н. A statistical study of the geoeffectiveness of magnetic clouds during high solar activity years Hi. Geophys. Res. V. 109. A09101. doi:10.1029/2004JA010410. 2004. [3] E.K.J. Kilpua, Y. Li, J.G. Luhmann, L.K. Jian, C.T. Russell. On the relationship between magnetic cloud field polarity and geoeffectiveness // Ann. Geophys. V. 30. P. 1037-1050. doi:10.5194/angeo-30-1037-2012. 2012 [4] Kroll N., Trajvelpis A. Basics of Plasma Physics. М.: Mir, 1975. 525 c. (in Russian) 77