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.

“P h y sic s o f A uroral P h en o m en a ”, Proc. X X X V I A n n u a l Sem inar, A p a tity , p p . 7 7 - 80, 2 0 1 3 Poiar © Kola Science Centre, Russian Academy of Science, 2013 institute*'031 MODULATION OF TEC/GPS BY ULF Pc5 WAVES V. Pilipenko1, V. Belakhovsky2, D. Murr3, E. Fedorov4, M. Engebretson3 1Space Research Institute, Moscow 2Polar Geophysical Institute, Apatity 2Augsburg College, Minneapolis 4Institute o f Physics o f the Earth, Moscow Introduction The terrestrial ionosphere represents an inner boundary of the space environment where the transition from the neutral atmosphere to the ionized gas of space occurs, and where the transfer o f energy through the coupled magnetosphere-ionosphere system takes place. The interaction between the solar wind and magnetosphere provides a rich source for various types of ULF waves, which are always present in the magnetosphere and ionosphere. Historically, ULF wave properties have been deduced from ground-based magnetometer arrays, supplemented by magnetic measurements from various spacecraft. Nowadays local variations of electron density caused by long- period ULF waves can be detected by ionosphere sounding techniques: Doppler sounders, SuperDARN radars, riometers, etc. The ever-growing facilities o f GPS monitoring systems provide information on variations of a radiopath-integrated ionospheric parameter - the total electron content (TEC). GPS/TEC observations are becoming a global technique to monitor the propagation o f waves and transients along the ionosphere. Early results reported related geomagnetic variations in the ULF band with TEC fluctuations. Davies and Hartman [1976] reported two cases where the change in TEC was associated variations in the ULF Pc4 range. A more comprehensive analysis by Okuzawa and Davies [1981] showed that variations in TEC with similar periods as in ground magnetometer records. However, the mechanism of TEC modulation by geomagnetic pulsations has not been established. In this paper, we demonstrate that TEC/GPS technique is sensitive enough to detect intense Pc5 pulsations at high latitudes. Observational data We use the slant TEC data with 30-s resolution from the array of GPS receivers in Scandinavia (Fig. 1). As a measure of path-integrated plasma density NT the TEC units (1 TECU= lxl016 e/m2) are used, and TEC variations are given in the percentage Д NT / JVT x 100%. Magnetometer data from the IMAGE array, covering the range of geographic latitudes from -79° to -58°, are used. KIR I M '.S Fig. 1 Intersections of radio paths from GPS satellites S07 and S09 to ground receivers KIR and VARS in Scandinavia with the ionosphere at altitude 250 km. Magnetometers are denoted with triangles, GPS receivers are denoted with squares. Red stars along orbit projections denote time moments 11.00, 12.00, 13.00, and 14.00 UT. 31 October event During the 2003 “Halloween storm” the superposition of 3 extremely large magnetic storms occurred on Oct. 29-31, caused by an extremely fast coronal mass ejection. During the recovery phases of these storms very intense global Pc5 waves were observed. In this study we concentrate on the Oct. 31, 2003 (day 304) event. During this event the global character of Pc5 waves is most pronounced: coherent quasi-monochromatic variations are observed over a wide range of CGM latitudes, from ~70° to ~50° during morning and post-noon hours in Scandinavia. During the 11-14 UT period with elevated Pc5 activity, TEC fluctuations detected by receivers at KIR and VARS from GPS satellites S07 and S09 have been compared with ground geomagnetic variations. The raw TEC data show gradual variations around Nx~30-40 TECU with superposed small-scale fluctuations. To highlight these fluctuations the TEC data have been detrended by high-pass filtering with a cut-off frequency of 1 mHz. The comparison o f TEC fluctuations with magnetic variations at KIR shows the occurrence of persistent TEC periodicity nearly on the same time scale as geomagnetic pulsations (Fig. 2). The peak-to-peak amplitudes of oscillations of the 77