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.

Fluctuations in the solar wind density and IMF It is also seen that the maximum of the ULF_N was observed under low values of the SW speed at the phase of its increasing. The ULF_N maximum was ahead the ULF_B maximum at ~ 4 hours. Two examples (22-24 January 2006 and 10-12 July 2007) of the high-speed SW streams passage are shown in Fig. 4, there are shown (up to down) the time variations of SW velocity (V), SW density (Np), IMF total magnetic field (B) obtained from 1-min OMNI database and the calculated the ULF-index for the SW density ( ULF_N) and IMF В ( ULFJB). 22-24.01.2006 10-12.07.2007 Fig. 4 Two example of the SW speed (V), SW density (Np) and the level of fluctuations of the SW density ( ULF_N) and IMF В (ULF_B) during the passage of high-speed streams. The examples in Fig. 4 demonstrate the general properties of the HSSs front edge structure, confirming those established by our statistical analysis: the amplitude maximum o f the (2-7) mHz fluctuations in the SW density (ULF_N) and its temporal slop followed the time variations of SW' density (Np) and the same for the ULFJ3 and IMF B. It is seen that density increases was gradual. It means the storm initial phase begins gradually without sudden impulse (SC). The SW density dramatically drops at the SW stream interface. The variations of the ULFJB and IMF В have bell-like slope with maximum around the SW stream interface. 3. Discussion As it is known that CIRs are produced when the outward of the Sun flowing fast wind (HSS) overtakes the outward flowing slow wind, an oblique region of compression and velocity shear results. Beyond the CIR there is the slow solar wind. Along the center of the CIR is the stream interface, i.e. a boundary between slow and fast solar wind [e.g., Forsyth and Marsch, 1999; Borovsky and Denton, 2010]. CIR interaction with the Earth’s magnetosphere produces only weak to moderate intensity magnetic storms. Our analysis o f the SW density and IMF В distribution associated with HSSs space structure showed (middle panel in Fig. 2) that 24 hours prior to the SW interface boundary (in the area of slow wind), the SW density and its fluctuations (ULF_N) were twice higher than 24 hours behind this boundary (in the area of fast wind). The Np maximum was observed a few hours before the stream interface. Some authors [e.g., Richter and Luttrell, 1986; Borovsky and Denton, 2010] also found that the SW plasma number density (Np) is peaking prior of to the stream interface on the slow SW side. The middle panel in Fig. 2 also demonstrates that the IMF В maximum was located in the interface area. The same results was obtained by [Richter and Luttrell, 1986; Borovsky and Denton, 2010]. 115