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.

Polar “Physics o f Auroral Phenomena", Proc. XL Annual Seminar, Apatity, pp. 76-77, 2 0 1 7 W / i l i Geophysical ' Polar Geophysical Institute, 2017 Institute POSSIBLE CAUSE OF SOLAR WIND MAGNETIC CLOUD SHOCK WAVES N.A. Barkhatov1, E.A. Revunova2, A.B. V inogradov1 1Nizhni Novgorod State Pedagogical University, Nizhni Novgorod, Russia zNizhni Novgorod State University o f Architecture and Construction, Nizhni Novgorod, Russia Abstract. The work to the study of the condition and possible causes of the appearance of shock waves on the Solar wind magnetic cloud front is devoted. It is known that magnetic clouds are one of the most geoeffective plasma streams, since they become sources of mostly strong geomagnetic disturbances. Studies shows that the geoeffective properties of magnetic clouds increase with the presence of a shock wave and a shell before them [1]. A simultaneous abrupt increase in the parameters of Solar wind (velocity, concentration, temperature) on the magnetic cloud shock wave is noted. It is followed by a region with fluctuations of interplanetary magnetic field (IMP) components and increased density, called the magnetic cloud cover. The study was carried out on 75 events registered in near-Earth space from 1973 to 2012 (according to the satellite system OMNI, http://cdaweb.gsfc.nasa.gov/istp_publicf) and identified in the literature as magnetic clouds [2,3]. Previously, a visual analysis of the dynamics of the Solar wind parameters in front of magnetic clouds to detect shock waves in front of them according to their distinctive features was performed. As a result, it was found that 30 examined clouds had no shock waves, and the remaining 45 they were accompanied. The velocities o f the sound waves Vs and Alfven waves Va are compared with the relative velocities Vrel of magnetic clouds to the Solar wind to determine the conditions under which shock waves appear before the magnetic clouds. The sound and Alfven wave velocities were calculated on the basis of the expressions given on the resource [http: //cdaweb. gsfc.nasa.gov/istp_public/] together with data on Solar wind parameters: Vs = yj0.12(T + 1.2 * 10s), Va = 20fi/Vn, where T is the temperature o f Solar wind plasma (К), В is the magnetic field induction (Tl), and n is the concentration of Solar wind plasma (m-3). ^ The relative velocity o f Solar wind magnetic a clouds as the difference between the velocities o f the 150 / cloud and the mean value of the velocity o f Solar ■g wind ahead o f it (for clouds without shock waves) or WG r before the shock wave (for clouds with shock waves) „ * * was calculated. The resulting ratios o f sound velocity T* 5" ** * Vs and Alfven velocity Va with the relative velocity 0 of magnetic clouds are shown in Figs. la and b, -ISO 100 -50 0 50 i00 150 200 250 300 350 respectively. In Fig. 1, the gray triangles correspond Vrel, km /s to magnetic clouds without shock waves, black circles - to magnetic clouds with shock waves, the k straight line corresponds where the velocities is equality. From these relations it follows that for magnetic clouds without shock waves their relative velocity Vrel is lower than the velocities o f the sound A # ® * waves Vs and Alfven waves Va (the gray triangles in Л М M • # * * Figs. 1and b are located near the ordinate axis). There i y - / * * * is an excess of the relative velocity of clouds over -150 -100 -50 0 50 100 150 200 250 300 350 andA ltonvelocitiesformagaeticcloudsw ith shock waves (black circles in Figs. la, b). These data Vrel, km/s lies below the direct line (Fig. la, b) which corresponding to the equality o f velocities. At the Figure 1 same time, relative velocity of clouds with shock waves exceeds 50 km/s. It is known that the boundary of the plasma formation remains fixed under the condition that the sum o f the gaskinetic nkT and the magnetic p*=B2l2\io pressures on it is equal [4]. The displacement o f the boundaries like expansion or contraction o f the given formation, arises as a 200 </) 150 200 & > 50 76