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.

“P hysics o f Auroral P henom ena", Proc. XXXIII A n nua l Sem inar, Apatity, pp. 91 - 94, 2011 © Kola Science Centre, Russian Academy of Science, 2011 Polar Geophysical Institute THE FORECAST OF GEOMAGNETIC ACTIVITY UNDER THE ESTABLISHED CHARACTERISTICS OF SOLAR WIND MAGNETIC E.A. Revunova1, N.A. Barkhatov1, A.E. Levitin 3 1 Nizhniy Novgorod State Pedagogical University, 603950 Nizhny Novgorod, Russia 2 Pushkov Institute o f Terrestrial Magnetism, Ionosphere and Propagation o f Radio Waves (IZMIRAN), Russian Academy o f Sciences, 142190, Troitsk, Russia Abstract. The influence analysis of magnetic cloud orientation and axis magnetic field on its geoeffective properties carried out. The magnetic cloud as force-free cylindrical flux rope is considered. The task of the short­ term forecast of geomagnetic storm intensity expected at interaction of magnetic clouds with Earth’s magnetosphere is considered. The forecast is basis on method of cloud parameters definition on few initial magnetic field components measurements on spacecraft. Well known connection geoeffective Bz component of Interplanetary Magnetic Field (IMF) vector with Dst-index geomagnetic activity take in attention. 1. Introduction Source of the most geoeffective disturbance are coronal mass ejections (CMEs). At the motion to the Earth they often take closed formations with original plasma and magnetic field behavior in them. They are magnetic clouds [Bothmer et al., 1998]. Magnetic clouds are structures with magnetic field high amplitude, low temperature and low value (3-plasma and monotonic rotation of magnetic field vector [Burlaga et al., 1981, Lepping et al., 1990]. Interest to The actual study o f magnetic clouds is connected with their potential geoefficiency. They can contain magnetic field with large-amplitude vertical component Bz<0. That is the reason of significant growth geomagnetic activity during interaction of Earth’s magnetosphere with cloud [Echer and Gonzalez, 2004]. In present time several models of magnetic clouds are developed [Romashets and Vandas, 2001; Vandas et al., 2002; Hidalgo et al., 2002]. The most widespread approach for cloud magnetic field modeling is force-free approach. It assumes that currents in cloud are parallel (or antiparallel) to force-lines of magnetic field, and perpendicular current component is absent. All developed approach will be coordinated with each other. Complication of model does not contribute to essential elaboration of key cloud parameters [Hidalgo et al., 2002]. Therefore in the given study force-free cylindrical model of clouds is used. The analytical expressions which describing behavior of magnetic field components inside such modeling cloud in coordinate solar-ecliptic system are received in [Barkhatov et al., 2009]. In this approach magnetic field cloud configuration is described of parameters: value of magnetic field on cloud axis, cloud radius, distance from line Sun-Earth to cloud axis (impact parameter), cloud axis orientation to ecliptic plane and magnetic field chirality. Cloud axis orientation to ecliptic plane is determined by polar and azimuthal angels. Magnetic field chirality indicates direction of its rotation in cloud. Usually the analysis of magnetic clouds is carried out after they have completely passed through spacecraft, and, consequently, through Earth’s magnetosphere [Wu and Lepping, 2002, Zhang et al., 2004]. However if you know magnetic field configuration of cloud approaching to the Earth, forecast intensity of expected geomagnetic storms is possible. In given study determination ranges of magnetic cloud parameters responsible for generation of various intensity magnetic storms are carried out. Development and testing technique of short-term forecast of geomagnetic storm intensity, expected at interaction of cloud with the Earth is carried out. 2. Base of force-free cylindrical model magnetic clouds For analysis of magnetic cloud parameters and development of short-term forecast technique of expected geomagnetic storm intensity the base of modeling magnetic clouds has been created. The total quantity of modeling magnetic clouds is about 2 000 000. Each of modeling magnetic cloud corresponds to certain set of parameters. Ranges o f modeling cloud parameters are established on the analysis of experimental data for real cases Solar plasma measurements from spacecrafts ACE and WIND from 1998-2001 [Lynch et al., 2003, Zhang et al., 2004]. In result, we selected following ranges of modeling cloud parameters: magnetic field on cloud axis -40 <Bo <41 nT (ДВо=9 nT); radius 1 500 Re <Ro <4 992 Re (ARo=388 Re); azimuthal and polar angles 0° <(3, s <180° (Др, e =20°); impact parameter -1 250 <b < 1 252 (Ab=278Re); average velocity of cloud 350 <V <650 km-s -1 (AV=100 km s-1), time interval passage spacecraft through cloud 10 <t <30 hours (At=5 hours). On the basis such change ranges of magnetic cloud parameters base of modeling clouds has been created. CLOUD 91