Physics of auroral phenomena : proceedings of the 39th annual seminar, Apatity, 29 February-4 March, 2016 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2016. - 167 с. : ил., табл.

SOLAR SOURCES OF INTENSIVE GEOMAGNETIC STORMS DURING THE 23rdSOLAR ACTIVITY CYCLE N .M . R udneva1, L.A . D rem ukhina2, P.M . Svidsky1, A .F. K harchiladze2 1Fedorov Institute o f A pp lied Geophysics, Moscow , Russia 2Pushkov Institute o f Terrestrial Magnetism , Ionosphere a n d Radio Wave P ropagation RAS, Moscow , e-mail: drem ukh @izm iran.ru Abstract. The analysis of the solar sources of 66 intensive (- 200 nT < Dst < -100 nT) and 16 very intensive (extreme) (Dst < -200 nT) magnetic storms and their localization on synoptic maps of large-scale solar magnetic field during the 23rd solar cycle (1996-2009) was performed. Coronal mass ejections (CME), coronal holes and filaments were considered as solar sources of geomagnetic storms. The study confirmed the existing opinion that extreme Dst-decrease is mainly associated with coronal mass ejections (CME) of type "halo". It was shown that effective solar flares (accompanied by CME) are localized at the boundaries of open magnetic field lines (sector’s and subsector’s boundaries). During the 23rd solar cycle, as in the past cycles, extreme storms occurred near the maximum of solar activity and its decay phase, and were caused by "halo"-type CMEs, accompanied by flares and filament’s disappearances. Geoeffective CME were located mainly near the Sun’s central meridian, and their solar wind had a speed more than 700 km/s. Very intense magnetic storms always associated either with strong or weak flares. Disappearances of filaments, not accompanied by flares, don't cause of intensive magnetic storms, in about 90% of events. All flares and the filament’s disappearances, followed by a development of intensive or very intensive magnetic storms, occurred on the boundaries of sub-sectors (OR-regions) or near projection of the heliospheric current sheet. In the reviewed period also coronal holes led to the development of intensive magnetic storms only in every seventh case. Introduction Since ancient times geomagnetic storms were divided into two types: the sporadic and recurrent. Sporadic disturbances with sudden onset are associated mainly with solar flares. As sources o f recurrent disturbances, repeating every 27 days, deemed "coronal holes" - areas on the Sun with a low radiation in the ultraviolet range and with radially directed magnetic field lines, which were discovered by “SKYLAB” [ Ilundhausen , 1980]. Their connection with high-speed solar wind streams was later shown [Svalgaard, 1977; Sheely and Harvey, 1981]. A lot of works is dedicated to study of the solar sources of geomagnetic disturbances. Authors of [Joselin and McIntosh, 1981; Joselin, 1986], on the base of analysis of 65 geomagnetic storms with maximum values of the Ap index >30 for the period from June 1976 to June 1979, have established the following frequency of occurrence of solar events previous 2-4 days intensive storms: solar flares - 40%, coronal holes - 52%, filament’s disappearances - 65%, and 8% storm’s sources were not identified. Most of the storms were caused by a combination of two or three sources. Satellite observations on the space station "SOHO" allowed to detect of coronal mass ejections (CME) [Yahiro et al., 2004], that turned out to be directly responsible for the develop of geomagnetic storms. Statistical studies [Webb et al., 2000; Wang et al., 2000; Zhao and Webb, 2003; Srivastava and Venkatakrishnan, 2005; Kim et al., 2005] have shown that the majority of CMEs are accompanied by solar flares or disappearance of filaments, and that not every CME causes a geomagnetic disturbance. Authors [Srivastava and Venkatakrishnan, 2005] have shown that 82% of extreme storms during 1996-2002 were related to CME s ”halo"-type or "partial halo"-type). The intensity of magnetic disturbances depends on the value of the South component (Bs) of the interplanetary magnetic field (IMF). An intensity and duration Bs, related with CME, is determined by the configuration of CME, as well as by its size and orientation relative to the Earth [Tsurutani et al., 1988; Lepping et al., 1990]. Study of solar structures, responsible for generating CME, was conducted in [Zhao and Webb, 2003]. The authors determined that 40 geoeffective CME in 1998-2000 were located predominantly in the areas over the bipolar coronal streamers between coronal holes with opposite polarities. It is also known that the complexes of solar activity tend to be on sector boundaries - the boundaries between areas of large-scale solar magnetic field. Areas that characterizing by open lines of force of photospheric magnetic field (sub-sectors or OR-regions) were investigated in [Ivanov and Kharshiladze, 2002; Ivanov et al., 2005]. In these studies it was been shown that the series extrastorms in the summer of 2000 were caused by active dynamics of OR-regions. The study of magnetic fields on the Sun in the periods of individual storms also allowed to conclude that active education, responsible for flares and CME, tend to be located at boundaries OR- regions [Ivanov and Kharshiladze, 2002]. In this paper we analyzed the solar sources of intensive and very intensive storms, registered in the period 1995-2009. In contrast to [Srivastava and Venkatakrishnan, 2005] we looked at not only CMEs as sources of magnetic storms but also coronal holes and filaments and their localization on synoptic maps of the large-scale magnetic field of the Sun. “Physics o f Auroral Phenom ena ”, Proc. XXXIX Annual Seminar, A patity, pp. 19-22, 2 0 1 6 © Polar Geophysical Institute, 2016 Polar Geophysical Institute 19