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.

ULF activity in the auroral oval as observed by the microsatellite Astrid-2 and the Greenland chain 990214A U . / ^ ----------- : El 1 E2 61 1, ! у ~ ^ Л i - v — i I ..........................: f . . . : j \J% Fig-2. The estimated FAC and high-pass filtered (cut-off frequency 0.1 Hz) components of electromagnetic burst in GEI coordinate system recorded by Astrid-2 on 14.02.99, 11:13:40-11:14:18 UT. 2-rd and 3-rd panels are electric components (El, E2), three lower panels - magnetic components (Bl, B2, B3). Рл A = 0 During its derivation it was assumed that the transverse gradient of the wave field is large, V x » 9 , .When p d —> 0 this equation reduces to local dispersion relation for Alfven wave COA = k V A . In the vicinity of resonant point x=0 the radial profile of Alfven velocity can be approximated as a linear function with the typical scale L: f ; 2( * ) = f ; 2( 0 ) ( i + x / l ) Then, this equation transforms into the following dx2 L y Exact solution of this equation can be obtained via Airy functions [Chen and Hasegawa, 1974]. However, an estimate of typical scale of the solution behavior near the resonant point can be obtained even with a simple scaling, as follows A = ( P d ^ ) - P d {L / P d f'* • Thus, the actual scale of the quasi-periodic KAW resonantly excited in MAR is determined not by pd, as often assumed, but by a larger value, Д. Thus, in a dispersive MAR the typical scale of resonant oscillations in saturation state and quality factor are л = М /3 Q M L / P d f Actual influence of dispersive effects is determined by the integrated over the field-aligned wave structure parameter <Pd>. At small altitudes, R<2 RE, its reasonable estimate is <pd> ~ <A,e> ~ 0.5 km. Assuming that L~10- 400 km, we obtain that the expected scales of DAW are Д -1.4-5 .8 km, which are to be detected by a low-orbiting satellite with V 0 ~ 7 km/s as a burst at frequency/ ~ 1.2-5.0 Hz. Identification of Disturbance Physical Nature from Multi-Component in-situ Observations The modified apparent impedance, or impedance velocity (ratio between orthogonal electric E ± and magnetic B± components) can be used to identify the physical nature of disturbances: Mo B ± For quasi-steady 1-dim FAC sheet the amplitude part of impedance is U ( со,к ) = VP = ( / / 0£ я ) is ionospheric Pedersen velocity. For travelling shear Alfven wave with = 0 the apparent impedance is U (со, k ) = VA . For standing shear Alfven wave in the MAR U depends on altitude z, and varies in the range Vp <| U |< VA(VA / Vp) . The characteristic feature of impedance is that it does not depend on spatial scale of disturbance. Hence, during satellite observations the experimentally observed values U(f) should be frequency independent. In DAW the 73