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.

Polarization o f sm all-scale magnetic perturbations in the topside auroral ionosphere in the e ve n ts o f broadband ELF turbulence Mathematically, the lack of coherence between two orthogonal components bx and bv of vector bL can be verified by a transition to analytical signals bxr + i bxi and byr + i byi via Hilbert transform and calculations of correlation coefficients r, = r(bxr, byr) (testing for linear polarization) and rc = r(bxn byJ) (testing for circular polarization). Table 1 contains coefficients r, and rc calculated with applying the Spearman rank correlation procedure to the magnetic components bN and bE observed in the event of BB ELF turbulence displayed in Figure 3b at UT = 07:03:10-07:03:14 that were filtered in three pass bands. We note that Spearman rank correlation coefficient r is a conventional measure of correlation between two arbitrarily distributed samples. With correlation coefficients Г/ and rc known, we tested the null hypothesis that the considered magnetic components are not correlated (H = 0) against an alternative that they are correlated (H= 1). The significance level p was taken 0.01, which corresponds to one false decision against 99 true decisions. It is seen from Table 1 that a suggestion of circularly polarized signal must be rejected ( Hc = 0 in all cases). As for the linear polarization, while in two of three cases # / = 1, indicating statistically significant value of coefficient rh the coefficient itself is low. Therefore, we conclude that only a minor part of the signal is linearly polarized. Figure 4. Hodograms of the perpendicular magnetic field b± = (bN, bE) observed in the event of BB ELF turbulence shown in Figure 3b and filtered in different passbands. The vector lengths are in relative units. 49