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.

“Physics o fAuroral Phenomena" Proc. XXXIIIAnnual Seminar, Apatity, pp. 33 - 36, 2011 © Kola Science Centre, Russian Academy of Science, 2011 Polar Geophysical Institute DAYSIDE STORM-TIME ULF PULSATION IN THE SOLAR ACTIVITY MINIMUM 0 .V . Kozyreva1and N.G. K leim enova1,2 1. Institute o f Physics o f the Earth RAS, Moscow, Russia 2. Space Research Institute RAS, Moscow, Russia Abstract. The dayside ULF-pulsation activity has been analyzed during the selected succession of 10 recurrent magnetic storms (CIR-storms), repeated with the periodicity o f about 27 days in 2006. This time corresponds to the solar activity minimum. The ULF-index, characterized the wave activity in the frequency range 2-7 mHz, was calculated according to the ground-based 1-min observations at the pre-noon (03-12 MLT) and afternoon (12-18 MLT) sectors for auroral (60-70°) and polar (70-90°) latitudes. It was found that in all phases of the magnetic storms under consideration, the maximum of the enhanced ULF-activity was observed at the polar latitudes (>70°). In the studied CIR-storms, the value of the solar wind velocity was very large (more 600 km/c) provided the Kelvin- Helmholz instability enhancement and correspondingly the ULF wave generation. The comparison of the ULF- activity during the CIR-storms (typical for the solar activity minimum) and CME-storms (typical for the solar activity maximum) showed that the ULF-activity associated with the CIR-storms was observed at the higher latitudes then in the CME-storms. 1. Introduction It is known [e.g. Tsurutani et al, 2006] that in the years of the solar activity minimum, the dominant solar phenomena affecting geomagnetic activity are high-speed streams (HSS) from the coronal holes. When HSS overtakes slow-speed stream, the interaction of the flows with different velocities forms a region of compression plasma, so called the “corotating interaction region” (CIR). In the maximum of the solar activity the most geoeffective structures of solar wind, which cause the magnetic storms, are the coronal mass ejection (CME) [e.g., Yermolaev and Yermolaev, 2002; Borovsky and Denton, 2006]. For the brevity, the magnetic storms, caused by CIR, we will call CIR- storms, and the storms, caused by CME - CME- storms. There are a large number of works, dedicated to a study of the differences between CME- and CIR- storms. For instance, [Borovsky and Denton, 2006] gave 21 differences between CME- and CIR- storms. They noted that in CIR-storms there are observed the more prolonged ULF pulsations related with the more prolonged time intervals with high solar wind velocity. Some authors [e.g., Singer et al, 1977, Rostoker et al, 1998; Engebretson et al, 1998; Mathie and Mann, 2000, 2001; O' Brien et al, 2001] also showed that both the amplitude and the probability o f the ULF waves in the range o f the Pc5 pulsation (f-2-7 mHz) grows with an increase of solar wind velocity. In our previous works [Kozyreva and Kleimenova, 2004, 2008, 2009] we showed that the initial phase of CME-storms is characterized by the excitation of the Pc5-6 pulsations (T-5-20 min) with the greatest amplitude in the morning sector o f the polar cap. During the main phase of CME-storms wave Pc5-6 activity is shifted into the region o f the closed magnetosphere. The aim of this work is to study the global spatial distribution of dayside Pc5 geomagnetic pulsations during the different phases of the CIR-storms, developing in the minimum o f the 23rd solar cycle. 2. Data and results For the analysis we selected 10 sequential recurrent storms (CIR-storms) in 2006 (year of the minimum of the 23rd solar cycle). The list of the analyzed storms is given in the Table, where for each storm we show the minimum values of Dst, the solar wind density prior to the storm beginning (N0) and its maximum (Nniax) in the compression region, the minimum value of the solar Table. Characteristics of the analyzed storms № Date ^Stnljn nT N0 cm '3 ^max CM3 V •vmin on/s Vvmax un/s 1 18-22.02.2006 -40 5 27 350 680 2 18-22.03.2006 -40 4 20 350 720 3 12-16.04.2006 -100 4 16 360 670 4 10-14.05.2006 -20 2 15 370 650 5. 06-10.06.2006 -40 5 42 350 650 6 04-07.07.2006 -30 6 50 340 620 7 31.07- 03.08.2006 -20 5 20 380 630 8 26-30.08.2006 -40 3 50 330 650 9 23-27.09.2006 -60 7 65 350 650 10 20-23.10.2006 -25 5 27 300 650 11 14-16.12.2006 -145 2 10 540 900 33