Physics of auroral phenomena : proceedings of the 38th annual seminar, Apatity, 2-6 march, 2015 / [ed. board: A. G. Yahnin, N. V. Semenova]. - Апатиты : Издательство Кольского научного центра РАН, 2015. - 189 с. : ил., табл.

“P h ysics o f Auroral P henom ena", Proc. XXXVIII A n nua l Sem inar, Apatity, pp. 11-14, 2 0 1 5 © Kola Science Centre, Russian Academy of Science, 2015 Polar Geophysical Institute INFLUENCE OF SLOPE OF THE SOLAR WIND INHOMOGENEITY FRONT ON PROPERTIES OF LONGPERIOD PULSATIONS DURING SSC Yu.Yu. Klibanova1,2, V.V. M ishin1, B. Tsegmed1,3, A.V. Moiseyev4 1 Institute o f Solar-Terrestrial Physics SB RAS, Irkutsk 2The A.A. Ezhevsky Irkutsky State Agrarian University, Irkutsk 3 Institute o fAstronomy and Geophysics o f the Academy o f Sciences o fMongolia, Ulan Bator, Mongolia 4The Yu. G. Shafer Institute o f Cosmophysical Research and Aeronomy SB RAS, Yakutsk Abstract. We study long-period geomagnetic pulsations caused by the arrival of the solar wind (SW) inhomogeneity front during the 14 July 2012 magnetospheric storm commencement from data of the ACE, WIND, THEMIS satellites, as well as ground stations, located at the low, mid and high latitudes. It is shown that the propagation direction of pulsations corresponds to the excitation mechanism by the front impact on the magnetopause, and the shift from the noon meridian of sector of waves running away is determined by an azimuth angle of the front inclination. A change in the polarization direction in longitude and latitude is observed. The rather high frequency of observed global pulsations / = 4.4 mHz is caused by the compression of the subsolar magnetopause to L = 6.7 and is not associated with SW fluctuations. Introduction The literature has accumulated extensive experience in the study of the basic mechanisms o f the long-period geomagnetic pulsations generation in the frequency range (1.67 - 25 mHz) due to the SW inhomogeneity front impact that caused the magnetospheric storm sudden commencement (Ssc) [ Pudovkin et al„ 1976, Nishida 1980; Korotova and Sibeck, 1994, Rae et al., 2005]. To date, access to the data of the global network of ground-based magnetometers, widely spaced on the surface o f the Earth with high temporal resolution, allows us to carry out a more detailed analysis of the properties of the impulsive (lasting several periods) long-period geomagnetic pulsations during Ssc. The impact of the SW inhomogeneity front on the magnetosphere excites surface waves on its boundary, observed on the Earth in a form of rapidly decaying train of longperiod geomagnetic pulsations. Tbeir propagation in the azimuth direction comes from the contact area of the magnetopause with: 1) the IMF plane [Korotova et al., 2002], when the SW pressure is homogeneous on the front, or 2) the front in the presence of Pd inhomogeneity on it [Mishin et al., 2013]. Activation of the substorm activity affects the propagation direction of waves, the distribution of their amplitude and polarization [Mishin et al., 2013; Klibanova et al., 2014]. The aim of this work is a detailed analysis of geomagnetic pulsations during the 14 July 2012 storm Ssc from the 1 s and 10 s geomagnetic data of ground stations located on not only high, but also the mid and low latitudes in a wide range of longitudes. Observations We analyze the 14 July 2012 event. Ssc was recorded at 18.09 UT according to Geomagnetic Indices Bulletin NGDC USA. Fig. 1 shows variations of the SW parameters and IMF. The time of the SW inhomogeneity front registration by the WIND satellite is shifted to match with the time of the sharp change of the geomagnetic field on ground- based stations, caused by the front. The SW dynamic pressure Pd changes from 1 to 6 nPa, the velocity component Vx - from 391 to 580 km/s, the IMF By - from 5.3 to 13.5 nT and the IMF Bz - from - 4 to - 9 nT. Geomagnetic activity index reached a value of 1311 nT. Ground-based observations show that the Figure 1. Variations of the IMF and the SW parameters at WIND (XGSE= 205 RE, YGSE= - 61 RE, Z gse = - 12 Re), and AE index. geomagnetic pulsations begin at 18.09 UT (from data of the station DAWS (07 MLT)). The azimuth angle of the front plane inclination (measured counterclockwise from the direction of the x-axis in the plane (x, y) of the GSE system (ie from the Sun) is equal to <p = 92.5° from data of satellites WIND and ACE (XGSE =230 11