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.

О. V. Kozyreva and N.C. Kleimenova Fig. 2 The results of the statistical analysis o f 63 HSSs: the mean values (solid line) and the standard deviation (dashed lines) of the SW velocity (V), SW density ( Np ), IMF ( В), and ULF fluctuations in the SW density ( ULF_N) and IMF В ( ULF_B ). To study the dependence of the ULF fluctuations level on values of the total field IMF В and SW density (Np) we selected the events with Npmax> 15 cm'3. The obtained results are shown in Fig. 1. Fig. 1 demonstrates the clear enhancement of the amplitude o f the maximal fluctuations in Np and IMF В (i.e. ULF_Nmax and ULF_Bmax) with increasing the values of the themselves Npmax and IMF Bmax. The statistical analysis of the level of ULF fluctuations (ULF_N and ULF_B ) in the high-speed streams in form of CIR has been performed by applying the superposed epoch method. We selected set o f the 63 events of the HSSs in which the maximal number plasma density (Npmax) in the region of compression was > 25 cm'3 and the solar wind speed ( Vmax) was > 450 km/s. Following to [ Borovsky and Denton, 2010], the passage of the stream interface (the boundary between the slow and fast solar wind in the CIR structure), i.e., the UT time when the rate of speed stream increase (dV/dt) was maximal (maximum in the plasma vorticity in term of [Borovsky and Denton, 2010]), was taken as a “zero” of epoch. The top panel of Fig. 2 shows the rise in the SW speed associated with the passage of the CIR. One can see in Fig. 2 that the averaged maximum of the fluctuations in the SW density ( ULF_N) coincides with the maximum of the Np, and the maximum of the fluctuation in IMF В (ULF_B) coincides with the maximum of the IMF B. Note that the magnetic field strength IMF В peaking near the stream interface (zero epoch) as it was shown previously by Richter and Luttrell [1986] and Borovsky and Denton [2010]. The mean values of the SW speed (V), ULF_N and ULF_B, calculated by the superposed epoch method of 63 events, are plotted in Fig. 3. Clearly, the mean value o f SW speed (top panel) in Fig. 3 demonstrates the trend of 63 various HSSs events: the solar wind is slow prior to the CIR passage, it quickly rises through the CIR, and is fast afterward. Fig. 3 The mean values o f the SW speed (V), ULF_N and ULF B. 114