Physics of auroral phenomena : proceedings of the 37th Annual seminar, Apatity, 25 - 28 February, 2014 / [ed. board: A. G. Yahnin, N. V. Semenova]. - Апатиты : Изд-во Кольского научного центра РАН, 2014. - 125 с. : ил., табл.

GEOMAGNETIC ACTIVITY OF MAGNETIC CLOUDS CONSIDERING SEASON OF YEAR N.A. Barkhatov1, A.E. Levitin2, E.A. Revunova1’3, A.B. Vinogradov1 1Nizhniy Novgorod State Pedagogical University, N izhniy Novgorod, Russia 2Pushkov Institute o f Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Moscow-Troitsk, Russia 3N izhny Novgorod State University o f Architecture and Civil Engineering, N izhn iy Novgorod, Russia 1. In troduc tion As a result, long-term observation of the geomagnetic activity the existence of its semi-annual variations, manifested in the spring and autumn in the form of peaks in the long-term average values of the various indices o f geomagnetic activity was established [ Cortie, 1912]. For explain this characteristic geomagnetic activity behavior during the year two sets of hypotheses is designed: the axial hypothesis and hypothesis equinox. Axial hypothesis to the change Earth's gelioprojection on the solar disk during the year is related [Cortie, 1912; Chapman and Bartels, 1940]. In spring and autumn, due to changes in rotation axis inclination of the Sun to the Sun-Earth line at ~ 7 °, the angular distance from the projection of the Earth to the Sun’s equator are maximized, and the Earth is more closely associated with zones of active regions (sunspot groups). They are grouped in the "royal" zones from 10 to 30 degrees north and south heliographic latitudes (see Fig. 1). Thus, in equinoxes times, with a maximum of latitude Earth's gelioprojection, are most likely to encounter the Earth with solar flux of active regions are recognized. Figure 1. Change latitude Earth's gelioprojection on the solar disk with the season depending December June March September According to the second group of hypotheses, geomagnetic activity increases when the angle between the Earth's dipole and Solar wind flow about 90° is observed. Here two models is recognized - the Kelvin-Helmholtz instability (Boller-Stolov model) and Russell- McPherron effect [Boiler and Stolov, 1970; Russell and McPherron, 1973]. In [Boiler and Stolov, 1970] Kelvin-Helmholtz instability occurs on the magnetosphere flanks, and its intensity depends on the daily and annual changes in the angle between Earth's dipole and Solar wind was shown. The maximum wave instability during the equinox (when the Earth's dipole is perpendicular to Solar wind flow), and the minimum - for solstice periods occurs. It is assumed that the observed at the magnetopause Kelvin-Helmholtz instability generates geomagnetic disturbances, which as semi-annual changes in geomagnetic activity are defined. Seasonal variation of geomagnetic activity within the Russell-McPherron effect is to increase the value of the interplanetary magnetic field (IMF) southward component in connection with its change in Solar-magnetospheric coordinate system with respect to the Solar-equatorial [Russell and McPherron, 1973] is explanation. According to him, the IMF in the Solar-equatorial coordinate system is formed, and the interaction of the IMF southern component with the magnetosphere in Solar-magnetospheric system occurs. These coordinate systems have a common axis X, which points to the Sun, and the Y-axis and Z are different rotation around of axis X. Thus, Bx component of the IMF will be the same in each system, and the values the components By and Bz during the transition from one coordinate system in another will change. This hypothesis does not exclude the axis model, since the Solar-equatorial system depends'on the Earth's heliographic latitude [Russell and McPherron, 1973]. All the hypotheses of seasonal variation of geomagnetic activity only the mutual orientation of the Sun, or the Solar wind and the Earth's dipole, without affecting the internal structure of the flows and their characteristics take into account. However, the structure of the plasma flow by the type of its Solar source is determined, and its effect on the Earth's magnetosphere on the relative position of the Solar source and the Earth also depends. Such geoeffective structures as magnetic clouds, in contrast to other plasma flows have pronounced orientation in space defined by the magnetic field lines of a sunspot group, which in turn are the most preferred location along the Solar latitude. That is why they sources of varying intensity magnetic storms during periods o f equinoxes and solstices can become. The hypothesis seasonal dependence of geomagnetic activity for the most geoeffective Solar flow o f magnetic clouds of the Solar wind proposed. They by the relative orientation of the axial magnetic field of magnetic clouds and the Earth's magnetic dipole is registered. In times of equinoxes and solstices the projection of an axial magnetic field clouds on the Earth's dipole are different. This should be reflected in the seasonal dependence of geomagnetic 78 *Physics o f Auroral Phenomena", Proc. XXXVII Annual Seminar , Apatity, pp. 78-80, 2014 © Kola Science Centre, Russian Academy of Science, 2014 Polar Geophysical Institute