Physics of auroral phenomena : proceedings of the 35th Annual seminar, Apatity, 28 Februaru – 02 March, 2012 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2012. - 187 с. : ил., табл.

V. Pilipenkoet al. electron inertia and FLR dispersion increase the value of an apparent impedance making the waves more "electrostatic" as compared with shear Alfven wave [Stasiewicz and Potemra, 1998] u (c o , к ) = vA 7 ( 1 + В Д ) ( 1 + * 1 а 2) The U must grow beginning from scales kLp d ~ o ( l ) . Parameter k±p d for DAW generated by a conversion process can be estimated as k1pd~ T ji ^L /pd) И~2лУ(27-9.3)~(Г7-23. Therefore, U(f) should be frequency- dependent, that is grows with/ starting from critical f ‘ ~ kV0 / 2 л - — (kLp d ) •As has been observed by Astrid- ^ P d 2 (Fig.3), beginning from f >J* ~few Hz, the impedance U(f) indeed becomes frequency-dependent and grows with frequency. The observed U(f) growing dependence is in accordance with the suggestion of Stasiewicz & Potemra [1998] that DAWs determine the spatial structure of electromagnetic turbulence down to scales -30 m. Fig.3. MEM spectra of two electric and magnetic components (upper plot) and the apparent impedance, derived from two orthogonal components, E2 and Bl). Conclusions We analyzed electromagnetic observations made onboard Astrid-2 over the Greenland array during periods of intense westward AEJ and ULF activity in the morning sector. Modeling of the ionospheric east-west currents from the ground magnetometer data shows that Pc5 activity tends to be localized in the same latitudinal range as AEJ. In virtually every pass of Astrid-2 through a gradient of geomagnetic field, indicating FAC occurrence, burst of wide-band noise is observed in both electric and magnetic components. These FAC and AEJ are parts of global magnetosphere-ionosphere current system. In the range 0.01-5 Hz power spectra of bursts have "colored-noise" form, corresponding to fractal hierarchy of spatial scales from few 100 km to few km. MEM spectral analysis of bursts reveals the spectral power enhancements at f~ 1-4 Hz, which correspond to spatial scales ~ few km. Apparent wave impedance exhibits a growing frequency dependence, indicating a presence of DAW. The observed electromagnetic pattern can be explained as a result of resonant conversion of MHD disturbances into DAWs at a magnetic shell conjugate to AEJ. Small-scale DAWs are totally screened from the ground by the ionosphere and could be detected on satellite only. The wave activity observed at the ground is a large-scale part of Alfven disturbances driven by an external broad-band source. The whole process may be visualized as a breaking of large-scale MHD wave approaching magnetic "shore" into small-scale electromagnetic "splashes". Acknowledgements. This research is supported by the Danish Research, Russian Fund for Basic Research (grant 10-05-93107), and Program 22 of Russian Academy of Sciences. References Chaston C.C., C.W. Carlson, W.J. Peria, et al., FAST observations of inertial Alfven waves in the dayside aurora, Geophys. Res. Lett., 26, 647, 1999. Hasegawa A., and L. Chen, Kinetic processes in plasma heating by resonant mode conversion of Alfven wave, Phys. Fluids, 19, 1924, 1976. Gary J.V., L.J. Zanetti, B.J. Anderson, et al., Identification of auroral oval boundaries from in situ magnetic field measurements, J. Geophys. Res., 103, 4187, 1998. Leonovich A.S., V.A. Mazur, Resonance excitation of standing Alfven waves in an axisymmetric magnetosphere (monochromatic oscillations), Planet. Space Sci., 37, 1095, 1989. Lysak R.L., Relationship between electrostatic shocks and kinetic Alfven waves, Geophys. Res. Lett., 25, 2089, 1998. Marklund G.T., L.G. Blomberg, S. Persson, Astrid-2, an advanced microsatellite for auroral research, Ann. Geophys., 19, 589,2001. Popov V.A., V.O. Papitashvili, J.F. Watermann, Modeling of equivalent ionospheric currents from meridian magnetometer chain data, Earth Planets Space, 53, 129, 2001. Stasiewicz К., T. Potemra, Multiscale current structures observed by Freja, J. Geophys. Res., 103, 4315, 1998. Streltsov A., W. Lotko, Small-scale "electrostatic" auroral structures and Alfven waves, J. Geophys. Res., 104, 4411, 1999. Apparent Wave Impedances 74