Physics of auroral phenomena : proceedings of the 39th annual seminar, Apatity, 29 February-4 March, 2016 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2016. - 167 с. : ил., табл.

*.P h y sics o f A u roral P h e n om en a ”, Proc © Polar G eophysical Institute, 2016 IONOSPHERE RESPONSE TO THE INTENSE ULF WAVES AS OBSERVED BY GPS/TEC AND EISCAT INSTRUMENTS V. Pilipenko V. B elakhovsky1, D. M u rr2, E. F edo rov1, A. Kozlovsky3 'institute o f Physics o f the Earth, M oscow 2Augsburg College, M inneapolis 1SodankyIa Geophysical O bservatory o f the University o f Oulu Abstract. Earlier studies demonstrated that the monitoring of the ionospheric total electron content (TEC) by global satellite navigation systems is a powerful method to study the propagation of transient disturbances in the ionosphere, induced by internal gravity waves. This technique has turned out to be sensitive enough to detect ionospheric signatures of magnetohydrodynamic (MHD) waves as well. However, the effect of TEC modulation by ULF waves is not well examined a responsible mechanism has not been firmly identified. During periods with intense Pc5 waves distinct pulsations with the same periodicity were found in the TEC data from high-latitude GPS receivers in Scandinavia. We analyze jointly responses in TEC variations and EISCAT ionospheric parameters to global Pc5 pulsations during the recovery phase of the strong magnetic storms on Oct. 31, 2003. Comparison of periodic fluctuations of the electron density at different altitudes from EISCAT data shows that main contribution into TEC pulsations is provided by the lower ionosphere, up to -150 km, that is the E-layer and lower F-layer. This observational fact favors the TEC modulation mechanism by field-aligned plasma transport induced by Alfven wave. Analytical estimates and numerical modeling support this conjecture. 1. Introduction The ionosphere represents an inner boundary of the near-Earth environment where the energy exchange occurs between the neutral atmosphere and the plasma of outer space. MHD waves provide an effective channel o f the energy transfer from the outer magnetosphere to the bottom of the ionosphere. The interaction between the solar wind and magnetosphere acts as a permanent source of various types of MHD waves in the ultra-low-frequency (ULF) band, which fill the entire magnetosphere and reach its inner boundary, the ionosphere. While ground magnetometers and magnetospheric satellites provided tremendous amount o f information about ULF wave properties in the magnetosphere and on the ground, the wave properties in the ionosphere remained unavailable to in-situ observations. The ever-growing array of global satellite navigation systems (GPS, GLONASS, etc) provide information on variations of a radiopath-integrated ionospheric parameter - the total electron content (TEC). The GPS/TEC technique turned out to be sensitive enough to detect ionospheric signatures o f ULF waves. The TEC modulation by intense Pc5 pulsations was found by [Pilipenko et al., 2014a; Watson et al., 2015]. Thus, the standard TEC/GPS technique is sufficiently sensitive to detect ULF waves in some cases. However, a physical mechanism of TEC periodic modulation associated with ULF waves has not been established yet. Here we analyze a unique event when the same global Pc5 waves were detected in the ionosphere by the GPS/TEC technique [Pilipenko et al., 2014a] and EISCAT radar [Pilipenko et al.. 2014b], We analyze these observations simultaneously which has provided an additional information on the relationship between geomagnetic and ionospheric variations. 2. Observational data We use the standard TEC data with 30-sec resolution from an array of GPS receivers in Scandinavia. The slant TEC along a radiopath can be converted into the vertical vTEC. denoted here as i VT, by assuming the altitude of pierce points to be 250 km. As a measure of columnar density NT the TEC unit (1 TECu=10 m ) is used. Magnetometer 10-s data from the IMAGE array, covering the range o f geographic latitudes from -79 ° to -58° are used (Fig. 1). The magnetometer observations are augmented with the multi-beam IRIS riometer data from Kilpisjarvi (KIL), that monitors a cosmic noise absorption caused by the energetic (>30 keV) electron precipitation into the ionosphere. The magnetometer data have been decimated to a common 30-s step with TEC data We use the data with 30-s cadence from the UHF radar EISCAT, comprising the receivers at Sodankyla (SOD) and Kiruna (KIR), and receiver-transmitter at Tromso (TRO) (Fig. 1). EISCAT radar beam was directed along the geomagnetic field line. Intersection of receiving paths from SOD and KIR is located nearly above the magnetic station TRO (68.0° N, 19.Г E) at altitude -290 km. This radar system enables one to determine the vector o f the ionospheric plasma drift velocity V and corresponding electric field E. The EISCAT radar system also measures the altitude profile of electron density Nc (z), ion temperature T{( z), and electron temperature Te(z ) along the beam up to -400 km. P olar . XXXIX Annual Sem inar, A patity, pp. 40-43, 2 0 1 6 Geophysical Institute 40