Physics of auroral phenomena : proceedings of the 36th Annual seminar, Apatity, 26 February – 01 March, 2013 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2013. - 215 с. : ил., табл.

“Physics o f Auroral Phenomena", Proc. XXXVI Annual Seminar, Apatity, pp. 1 1 3 -1 1 6 , 2013 © Kola Science Centre, Russian Academy of Science, 2013 Polar Geophysical Institute FLUCTUATIONS IN THE SOLAR WIND DENSITY AND IMF 0 .V . Kozyreva, N .G . Kleimenova (Institute o f Physics o f the Earth RAS, Moscow, Russia, kozyreva@ ifz. ru) A b stra c t. We studied the level of the ULF fluctuations in the frequency range of (2-7) mHz in the solar wind (SW) density (Np) and IMF by applying the special ULF-index, based on 1-min OMNI data. The set of the 63 evens of the high speed solar wind streams (HSSs) observed during the solar activity minimum (2006-2009) have been collected and analyzed. The superposed epoch method was chosen as our research technique. It was shown that the strongest ULF fluctuations in the solar wind density ( ULF_Np ) and in the IMF В ( ULF B) were observed at the front edge of the HSSs in the solar plasma compression region which leads to development o f a storm initial phase. The maximum o f ULF fluctuations in the SW density ( ULF_Np) was recorded under the relatively low values of the SW velocity during its increasing phase. The ULF_Np maximum was ahead (for ~4 hours) the maximum of the ULF_B. We found that both, the amplitude of the ULF_Np and ULF_B, increased with increasing the values of themselves Np and IMF В values. 1. In tro d u c tio n The interaction of solar wind (SW) and Interplanetary Magnetic Field (IMF) with the magnetosphere is one of the important problems of the geophysics. Now it is generally accepted that the main agents which transported disturbances from the Sun to the Earth's magnetosphere, are high-speed streams (HSSs) of the solar wind. During the minimum of the solar activity the HSSs are mainly originated from coronal holes, in which case the HSSs have the form of corotating regions of interaction (CIR) between slow and fast solar wind. The magnetic turbulence, especially in the ULF range (2-7 mHz), may play an significant role in the process of the energy transfer from the solar wind into the magnetosphere. Many authors have studied wave activity in the SW [e.g., Horbury and Balog, 2001; Walker, 2002; Kessel, 2008; Borovsky and Denton, 2010]. However, only few of them paid attention to effects of these waves on the geomagnetic pulsation generation [e.g., Walker, 2002; Kessel, 2008; Romanova and Filipenko, 2009]. The aim o f the current work is to statistical study the properties of the ULF (2-7 mHz) fluctuations in the solar wind density ( ULF_N) and IMF В ( ULFJB) during the passage of HSSs in form of CIRs which play a dominant role in geomagnetic activity during the solar minimum. 2006 - 2009 2006 - 2009 Fig. 1 The dependence of the ULF_Nmax on the Npmax in cm"3and ULF_Bmax on the Bmax in nT, where ULF_Nmax, ULF_Bmax, and Npmax, and Bmax are the maximal values of the ULF_N, and ULF_B, and Np and B, correspondingly, observed in a given day. 2. D a ta an aly sis The SW and IMF data collected during the solar activity minimum (2006-2009) have been analyzed. As research technique, we used the superposed epoch method, widely employed by many scientists. Earlier superposed epoch studies of CIRs can be found in the work of e.g., [ Richter and Luttrell, 1986; Denton and Borovsky, 2008; Borovsky and Denton, 2010]. Moreover, to assess the level of the ULF (2-7 mHz) fluctuations in the solar wind density (Np) and total magnetic field IMF B, we applied the special ULF-index, development by [ Kozyreva et al., 2007], based on 1-min OMNI data. 113