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.

“P hysics o fAuroral P henom ena”, Proc. XXXIII A n n u a l Sem inar, A patity, pp. 69 - 72, 2011 © Kola Science Centre, Russian Academy of Science, 2011 Polar Geophysical Institute CONTRIBUTION OF THE MHD WAVE MODES TO THE GLOBAL Pc5 PULSATIONS V.B. Belakhovsky V.A. Pilipenko 2, A.E. K o z lo v sk y 3 1- Polar Geophysical Institute, Apatity, Russia, E-mail: belakhov@mail.ru 2- Institute o f the Earth Physics, Moscow, Russia 3- Sodankyla Geophysical Observatory o f the Oulu University, Finland Abstract. The nature of so called global Pc5 pulsations is studied. The event with global Pc5 pulsations generated by quasi-periodic fluctuations of the solar wind dynamic pressure on 31 October 2003 is considered in detail. According to the ground magnetometer data Pc5 pulsations are observed both in the morning and afternoon MLT sectors. The physical mechanism of global Pc5 is supposed to be different from one o f the ordinary Pc5 pulsations associated with the shear Alfven oscillations of magnetic flux tubes. We also used the EISCAT radar data from the tri-static Tromso-Kinma-Sodankyla system allowing to calculate vectors of the F-region ionospheric plasma flow and electric field. The Pc5 frequency band pulsations are clearly seen in the variations of the Hall and Pedersen ionosphere conductivity, ionosphere plasma density, electron and ion temperatures, and the ionospheric electric field. For the time intervals when the Pc5 pulsations are observed on ground, hodographs of the ionospheric electric and ground magnetic fields have been compared. The angle between polarization axis of the electric and magnetic fields may show whether the pulsations are related to the Alfven mode or the magnetosonic wave. From these considerations we conclude that the morning and afternoon Pc5 pulsations are predominantly Alfven waves. These observations do not agrees with the statistical studies by Rostoker and Sallivan [1987] and Liu et al. [2009], who have shown that the morning Pc5 pulsations are caused mainly by the Alfven waves, whereas the afternoon Pc5 pulsations are mainly magnetosonic waves generated by the impulses of the solar wind dynamic pressure. Introduction During the recovery phase of strong magnetic storms the intense Pc5 pulsations which exceed the amplitude of ordinary Pc5 pulsations by the order of magnitude were observed [ Kleimenova, 2005; Belakhovsky, 2010]. These anomalous oscillations were named as the global Pc5 pulsations [Potapov, 2006] because they were observed in the morning and evening sectors simultaneously in a wide latitude range. The global Pc5 pulsations can exert a great influence on the dynamics of the relativistic electrons because their frequency is close to the drift frequency of MeV electrons [Elkington et al., 2003]. A large intensity, huge volume of the magnetosphere occupied by these pulsations, and the presence of the significant compressional component of the magnetic field - all these factors must lead to a more strong influence on the relativistic electrons (modulation, radial diffusion, acceleration) as compared with regular Pc5 pulsations. However, it is not finally known: do the global Pc5 pulsations have the same physical mechanism as ordinary Pc5 pulsations or they are caused by essentially different wave processes? In this study we provide some additional information on the properties of these pulsations using the simultaneous observations with ground magnetometers and EISCAT radar. Observations facilities The IMAGE and INTERMAGNET magnetometer data are used in this work. We also use the EISCAT radar data from the tri-static Tromso-Kiruna-Sodankyla system allowing to calculate the vectors of the F-region ionospheric plasma flow and electric field. To determine the solar wind and magnetosheath parameters ACE, WIND, GEOTAIL interplanetary spacecraft data are used in this study. The magnetic field data from GOES-10, GOES-12 geostationary spacecraft are used also. The event o f 31 October 2003 This event was well described in the previous papers [e.g., Panasyuk et al., 2004; Pilipenko, 2010]. Pc5 pulsations during 31 October 2003 observed by IMAGE stations were considered in detail by Kleimenova and Kozyreva [2005]. The global Pc5 pulsations were observed in the morning and afternoon MLT sectors. Frequency o f these pulsations was observed to be nearly the same at different latitudes, which may indicate a weak contribution of resonant effects into the spatial structure of global Pc5 pulsations. 69