Physics of auroral phenomena : proceedings of the 35th Annual seminar, Apatity, 28 Februaru – 02 March, 2012 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2012. - 187 с. : ил., табл.

“Physics o fAuroral Phenomena", Proc. XXXVAnnual Seminar, Apatity, pp. 85-87, 2012 © Kola Science Centre, Russian Academy of Science, 2012 Polar Geophysical Institute GEOMAGNETIC EFFICIENCY OF SOLAR EJECTION DEPENDED ON RELATIVE ORIENTATION OF SUN AND EARTH ROTATION AXES N.A. Barkhatov1, E.A. Revunova1, A.E. Levitin 2 'Nizhny Novgorod State University o fArchitecture and Civil Engineering, Nizhniy Novgorod, Russia ' Pushkov Institute o f Terrestrial Magnetism, Ionosphere and Radio Wave Propagation o f Russian Academy oh Sciences, Moscow-Troitsk, Russia A b stract. Work is devoted studying of causes of seasonal variation of geomagnetic activity. Its axial hypothesis based on change Earth helioprojection on Solar disk during year, due to change of an inclination of Solar rotation axis to Sun-Earth line is confirmed. As a result of carried out research of latitude distribution of Solar sources geoeffective coronal mass ejections their displacement during the equinox periods to zones of active regions which are the basic source of Solar plasma ejections is established. 1. Introduction Long study of geomagnetic activity showed presence of its semiannual variations, manifested as a maximum index of geomagnetic activity during the spring and autumn equinox [Chapman and Bartels, 1940]. To explain this variation developed several hypotheses. The main are axial hypothesis and equinox hypothesis. Axial hypothesis of semiannual variation of geomagnetic activity is associated with change Earth helioprojection on Solar disk during year [Cortie, 1912; Chapman and Bartels, 1940]. Due to change of inclination angle of Solar rotation axis to Sun- Earth line in direction to the Earth depending on terrestrial season on ~ 7°, in spring and autumn angular distance between Earth projection to Solar disk and Solar equator as much as possible. In these time-intervals Earth projection is located in zones of active Solar regions which are named in royal latitudes and settling down from 10 to 30 degrees northern and southern heliographic latitudes (fig. 1). During periods of winter and summer solstice Earth projection located around solar equator where active regions practically are absent. Thus, during equinox periods, when the Earth latitude of helioprojection is maximum, there is greatest probability to collision of Earth with Solar streams from active regions. December June March September Fig.l. Change in Earth latitude helioprojection on Solar disk, depending on season. Further studying of causes of seasonal variation of geomagnetic activity has led to occurrence of new hypothesis - equinox hypotheses in which inclination angle between geomagnetic dipole and Solar stream is considered. In an equinox hypothesis it is possible to allocate two basic models - Kelvin-Helmholtz instability (Boller-Stolov model) and Russell-McPherron effect [Boiler and Stolov, 1970; Russell and McPherron, 1973]. The hypothesis about Kelvin-Helmholtz instability suggests that daily and annual variation of angle between Earth dipole and Solar wind lead to generation of instability on magnetosphere flanks. As was shown in work [Boiler and Stolov, 1970] Kelvin-Helmholtz instability on magnetosphere flanks possesses semiannual variation, thus the instability maximum is necessary for equinox periods (when the terrestrial dipole is perpendicular to Solar stream), and a minimum - for solstice periods. In framework of equinox theory one more explanation of seasonal variation of geomagnetic activity was suggest by Russell and McPherron in work [Russell and McPherron, 1973]. The interplanetary magnetic field (IMF) of Solar wind arises in Solar-equatorial coordinate system (GSEQ), whereas its influence on magnetosphere and geomagnetic activity depends already on sign and amplitude vertical Bz components of vector IMF in Solar- magnetospheric coordinate system (GSM). These coordinate systems have general axis X which specifies to the Sun, and axes Y and Z have different rotation round an axis X. Therefore Bx component of IMF will be identical in each system, and values component By and Bz will vary at transition from one coordinate system to another. Thus, the given hypothesis explains semiannual variation of geomagnetic activity as increase southern components of IMF in connection with its change in Solar-magnetospheric coordinate system in relation to Solar-equatorial system. This phenomenon has been named Russell- McPherron effect. 85