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.

I. V. Golovchanskaya et al. Results The FAST magnetic experiment incorporated a tri-axial fluxgate magnetometer for dc and low-frequency magnetic field measurements, and a searchcoil system for measurements of ELF-VLF wave fields. For the purposes of the present study only fluxgate magnetometer observations are suitable, since the search coils have low sensitivity at frequencies below ~ 100 Hz [Elphic et al., 2001]. The frequency range here considered is restricted by ~ 0.5 Hz from below to avoid contamination from residual spin harmonics, and by ~ 8 Hz from above, which is dictated by low-pass filtering of fluxgate magnetometer data on FAST. Figures 3 shows three events of the BB ELF turbulence with typical duration of 50-100 s observed by FAST in traversals above the early morning auroral zone (Figure 3a), the afternoon auroral zone (Figure 3b), and the dayside cusp (Figure 3c) in the Northern Hemisphere. The despun along-track (bN) and across-track (bE) magnetic components, pointing, respectively, nearly northward and nearly eastward, are measured by the fluxgate magnetometer with a sample rate of 128 s'1 [Ergun et al., 2001]. It can be seen from the figures that the magnetic perturbations are polarized in the plane normal to the background magnetic field (the parallel magnetic component bz is small in all cases). Therefore, further we will focus on the bN and bE magnetic perturbations, which are relatively large in all three events (from tens of nT to a hundred of nT). Also shown is the along-track electric field component EN measured by the double probes on FAST with 512 s'1 sample rate. It is seen that intense electric perturbations tend to develop in the regions of magnetic field gradients. -wo •S 1 j ' PASTorbit OWOS *998-04-23 b. -40O -Ш ь / UT 22:03:20 22ЖМО 2Z04OT 2 2042D 22SM:<IO 22,-05:CO MLT 04:36 <11:40 0ЛЛЗ CM<31 1М:50 ОЗЯЗ Ш 7Й4 71,2 72,1 72,9 73.7 74.5 AIT 1741 17(56 («74 1642 1S»J 1561 IMO l03l> •d E SCO 4 ** 0 -Ж FASTorЬП 066D0 j / b 4 ^ -— * 1Д 07'.02M 07:0230 07ЛЗЯ0 0703:10 <37:0120 07.03:30 MLT 12:32 *2 *9 12:40 12*3 123? 12:30 ILAT 60.0 60S 700 70S 71.0 715 ALT 1040 10И 1067 J Ш 1006 1110 № 1CO FASTofb it 0661S A •? 0 % tel fi -10Q>- ~200 'C W tJT 20:2Cc20 20:20:30 202040 MLT 11*2 n;54 1 2M HAT a n BUB 81.3 20.20:50 2021:00 12Л 2 12;25 60.0 83.5 ALT ООЙ Dft4 «71 OSS 0*6 Figure 3. FAST observations of the BB ELF turbulence in traversals above (a) the early morning auroral zone; (b) the afternoon auroral zone, and (c) the dayside cusp; [Golovchanskaya et al., 2011]. To gain insight of polarization of magnetic perturbations under study, the hodograms of perpendicular magnetic fields b i = (bN, bE) have been constructed. Figure 4 displays those for bx = (bN, bE) observed in the event of BB ELF turbulence displayed in Figure 3b and filtered in different passbands. One can see that the polarization patterns are highly disordered, with changeable sense of polarization and unsteady phase relations. They have little in common with a repetitive, regular pattern expected for perturbations in the form of a plane linear wave [see Stasiewicz et al., 1998 for discussion]. 48