Physics of auroral phenomena : proceedings of the 34th Annual seminar, Apatity, 01 - 04 March, 2011 / [ed.: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 231 с. : ил.

"Physics o fAuroral Phenomena", Proc. XXXIV Annual Seminar, Apatity, pp. 71 - 74 2011 © Kola Science Centre, Russian Academy of Science, 2011 Polar Geophysical Institute THE DETERMINATION OF THE LATITUDE DISTRIBUTION OF THE RESONANCE FREQUENCY OF PC5 PULSATIONS FROM THE RADAR DATA V.B. Belakhovsky1, A.E. Kozlovsky2, V.A. Pilipenko3 1 Polar Geophysical Institute, Apatity, Russia 2 Sodankyla Geophysical Observatory o f the University o f Oulu, Finland 3 Institute o f the Earth Physics, Moscow, Russia Abstract. The event of 29 April 2001 was considered when geomagnetic Pc5 pulsations were observed in the morning sector at the latitudinal profile of the IMAGE magnetometers network. The following signatures of resonance properties were observed in the pulsations: the decrease of frequency of Pc5 pulsations with increase of the geomagnetic latitude and change of the phase and ellipticity during passage thought the resonance region. The beam of the VHF EISCAT radar in Tromso was inclining at 30° to the horizon and was directed northward toward Spitsbergen, so the increase of height along the radar beam was accompanied by the increase of the geomagnetic latitude. Clear Pc5 pulsations were observed in the line-of-sight velocity of the ionospheric plasma measured by the radar at 68 - 72 degrees of geomagnetic latitude that corresponded to the height of 100-410 km. There were no clear signatures of Pc5 pulsations observed in the density of ionosphere plasma and the ion and electron temperatures. The spectral analysis shows decrease of the frequency of Pc5 pulsations in ionosphere plasma velocity with increase of geomagnetic latitude, which is a manifestation of the resonance properties in the ionospheric plasma velocity. Thus, we show the possibility to determine the latitude distribution of resonance frequency of Pc5 pulsations from the radar data. 1. Introduction Geomagnetic Pc5 pulsations are the most powerful wave processes in the near-Erath space, which may distinctly modulate the magnetosphere and ionosphere plasma. The interaction of geomagnetic Pc5 pulsations with the ionosphere may be examined by the EISCAT radar. The radar allows studying the ionosphere with better spatial resolution than the ground-based magnetometer. The magnetometers register ionospheric disturbances of the scales larger than 100 km. Walker et al., [1979] were the first who measured the electric fields associated with geomagnetic Pc5 pulsations using the STARE radar. Later radars were utilized for studying so-called “ storm-time ” (poloidal) Pc5 pulsations with large (20-100) azimuthal wave number m [Allan et al., 1982]. The poloidal pulsations excited by proton clouds have different physical nature than the toroidal Pc5 pulsations. These Pc5 pulsations were weekly observed by ground magnetometers due to the shielding effect of the ionosphere. Most of the studies of Pc5 pulsations in ionosphere were done by using the coherent radars, like, e.g., SuperDARN radars. However, the coherent scatter radars usually do not provide continuous data (i.e., there are big data gaps in space and time). Another way is using the incoherent scatter radars EISCAT. The incoherent scatter radars may provide continuous measurements and allow determining not only the velocity of the ionosphere plasma but also ionospheric plasma density and temperatures of ions and electrons. Indeed, signatures of Pc5 pulsations were seen in the ion temperature [Lathuillere et al., 1986]. ]. In paper [Buchert et al., 1999] the authors seen the Pc5 pulsations in ionosphere plasma density and ionosphere conductivity. The pulsations in the ionospheric plasma density and conductivity were associated with poloidal geomagnetic pulsations. The resonance properties of Pc5 pulsations in the ionosphere were studied by [Walker, 1979, 1992]. Walker et al., [1979] have shown the presence of the phase shift of Pc5 pulsations in the ionosphere plasma velocity at latitude of resonance peak. Walker et al., \1992] used the SuperDARN radar in Goose Bay for studying ionospheric signatures of the ULF oscillations in mHz range excited by the field line resonance (FLR). They picked out the discrete frequencies 1.3, 1.9, 2.6, 3.3 MHz and supposed that the cavity mode may be responsible for the generation of these “magic” discrete frequencies. They investigate ULF pulsations at the night sector (01.00-04.00 MLT). However, on the dayside the manifestation of resonance properties of Pc5 pulsations in the ionospheric parameters is still an open question. In the present study we investigate the ionospheric manifestation of the large- scale (toroidal) Pc5 pulsations observed in the morning sector using the VHFESICAT radar in Tromso. 71