Physics of auroral phenomena : proceedings of the 37th Annual seminar, Apatity, 25 - 28 February, 2014 / [ed. board: A. G. Yahnin, N. V. Semenova]. - Апатиты : Изд-во Кольского научного центра РАН, 2014. - 125 с. : ил., табл.

“Physics o fAuroral Phenomena", Proc. XXXVII A nnual Seminar, Apatity, pp. 63-66, 2014 © Kola Science Centre, Russian Academy of Science, 2014 Polar Geophysical Institute GEOMAGNETIC Pci PULSATIONS IN THE SOLAR ACTIVITY MINIMUM N.G. Kleimenova, F.Z. Feygin, Yu.G. Khabazin, L.M. Malysheva (Schmidt Institute o f the Physics o f the Earth RAS, Moscow, Russia) Abstract. We studied the long-lasting (more 2 hours) series of Pci geomagnetic pulsations occurrence during the minimum of the solar activity (2006-2010) based on the ground-based induction magnetometer network at Scandinavia. It is known, that the Pci occurrence maximum is observed in the declining phase of the solar activity. Really, in the declining phase of the 23-th cycle of the solar activity (2006), the number of the hours with long- lasting Pel series was ~270. In the minimum between 23-th and 24-th cycle, the lowest value of the Wolf number (Wp) ~ 3 was observed in 2008 and 2009. However, in 2008 there were two sequences of recurrent magnetic storms with 13-14 storms in each, i.e. an overall about 30 moderate magnetic storms, but in 2009 there were only 5 small magnetic storms. Correspondingly, the number of the hours with long-lasting Pci series was -100 in 2008 and it was~20 in 2009. It supports the relationship of long-lasting Pci generation with magnetic storms development. We found that, generally, during the solar activity minimum, the shape of the dynamic Pci spectra looked like a very monochromatic emissions of not more 3-5 hours duration with a low central frequency (less than 1 Hz) and a narrow width of the dynamic spectra. However, during the declining (2006) and increasing (2010) phases of the solar activity, the spectral structure of Pci became more complicated and the duration of the Pci series increased up to 10-12 hours. The central frequency of the Pci series and the width of the wave dynamic spectra significantly increased. Sometimes it consisted of several varying frequency bands. The theoretical interpretation showed the width of the Pci spectra is controlled by an important magnetospheric parameter (ул / иЛ , where VA is the Alfven speed in the top of the magnetic field line, and Ц is the average field-along speed of the anisotropic protons. In trodu c tion The Pci geomagnetic pulsations are the repeated wave packets of Alfven waves in the frequency range 0.2-5.0 Hz travelling between the conjugated hemispheres. Their theory of generation and the morphological properties are widely discussed in the literature list time, e.g. in several revues [Gulielmi and Pokhotelov, 1994; Kangas et al, 1998; Demekhov, 2007]. The results of the last 10-years satellites (THEMIS, CHAMP, Cluster spacecrafts) measurements are presented in some papers, e.g. [Min et al., 2012; Park et al., 2013; Lin et al., 2014]. It is no doubt that Pel pulsations (“pearls”) are generated via the cyclotron instability o f radiation belt protons with anisotropic velocity distribution [Cornwell, 1965; Kennel and Petchek, 1966; Feygin and Yakimenko, 1971; and many others]. The ground-based data demonstrated the maximum of the mid-latitude (obs. Borok) Pci activity in the anti-phase with the solar activity [Matveeva, 1987], and the Pci activity in California, USA was strongest during the declining phase of a solar cycle [Fraser-Smith, 1970]. The rather similar results was obtained in the auroral latitudes (obs. Sodankyla, Finland), where the Pci occurrence rate appeared inversely correlated with solar activity with the phase delay of about two or one year [Mursula et al., 1991], which was explained in terms of magnetospheric ion composition [Guglielmi and Kangas, 2007]. Here we continue to study the Pci activity and their spectral properties using the wave spectrograms obtained from the ground-based induction magnetometer network at Scandinavia during the minimum o f the solar activity (2006-2010). Results Here we present the results of the analyzing the ground-based data of the magnetometer chain of Sodankyla Geophysical observatory, stored at ( http://sgo.fi/Data/Pulsation/pulArchive.php) . Fig. 1 demonstrated the solar activity during the discussed period. It is seen that in the minimum between 23-th and 24-th cycle (Fig. 1) of the solar activity, with the lowest value of the Sunspot number (Wp - 2-3) was observed in 2008 and 2009. The geomagnetic activity variation in 2008 and 2009 geomagnetic Pci pulsations occurrence is shown in Fig. 2. The magnetically quiets year was 2009. In 2008 there were two recurrent magnetic storm sequences with 13-14 storms in each (Fig. 2), i.e. an overall about 30 moderate magnetic storms. However, in 2009 there were only 5 small magnetic storms. It is seen, that in 2008 there were observed much more number of long-lasting Pci events than that in 2009. Most of Pci events were associated with magnetic storms and magnetic disturbances development. The long-lasting Pci pulsation series were observed mostly during the late recovery phase of magnetic storms and disturbances. 63