Physics of auroral phenomena : proceedings of the 38th annual seminar, Apatity, 2-6 march, 2015 / [ed. board: A. G. Yahnin, N. V. Semenova]. - Апатиты : Издательство Кольского научного центра РАН, 2015. - 189 с. : ил., табл.

V.V. Mishin etal. used the method of maximal contributions with short intervals Ax, <20 min and obtained a series of derivatives / 9Pdand &¥ / 3ESW depending on Pdand Esw. Fig. 3 shows graphs of these dependencies, built from three superstorms data. Saturation processes of 'P1 (Bz) and 4х! (Pd) are separated in time and can occur independently. Results for the three discussed events fit together and complement each other. The derivatives decrease exponentially when the value Esw and Pd continues to grow, confirming the VP 1 saturation effect for the strengthening SW. The SW electric field and the dynamic pressure depend on the SW velocity Vsw. In this regard, a question may arise about dependence from each other of parameters Pd and Esvv. Fig. 4 on an example of the 20 November 2003 event shows that for the interval (08:45 - 24:00) UT the SW velocity Vsw decreases very slowly. Our analysis has shown that in this interval the field Eswvariation is mainly determined by the change of non-radial IMF В = (By2 + Bz2) 1/2 (correlation coefficient Kcor (Esw, B) = 0.87), and the change in Pd - change in the density n (Kcor (Pd, n) = 0.93). Thus the Eswand Pdparameters can be considered independent on the whole interval superstorm (except SSC, when at the same time all the parameters change on the front SW inhomogeneity) and speak about the saturation of the polar cap magnetic flux and the Poynting flux f'from both of them separately. Figure 4. Solar wind velocity variation during the superstorm. Thus, the MIT results indicate the presence of 'F saturation under superstorm with continuous increase of not only Esw, but also Pd. Simultaneously with the saturation of ¥ there is slowdown of the Poynting flux ff'from SW to the polar ionosphere. Poynting flux: Comparison with MHD model Now we compare the results of MIT and the global PPRML MHD model. For the 20 November 2003 superstorm graphs of variation of a total energy flux and electromagnetic energy flux Qeim(Poynting flux) were calculated by the PPMLR MHD model. Fig. 5 shows the variation of the only electromagnetic flux 0 ,It. as its contribution to the total flux Q,n,*t amounted to more than 90%. It can be seen that: 1) for small values of Pd<5nPa and IMF Bz> -lOnT there is a growth of the power, and its values obtained by two models are close; 2) reaching a maximum at the P<i> (12-14) nPa, the Qeimflux does not increase further; 3) an increase in the flux depending on the southward IMF slows when Bz <-30nT and almost stops at values Bz<- 40nT, rarely observed during superstorms. For Bz<- 20nT, about half power, transported into the magnetosphere, penetrates into the polar cap (e'~0.5 Q ^ ). Figure 5. Variations of the Poynting flux: into the magnetosphere - Qeim (black dots and their approximating thick curves, obtained by the MHD model) and into the polar cap - s ' (circles, thin approximating lines, obtained by MIT) as a function of the dynamic pressure Pd and IMF Bz <0. On the saturation effect and finite compressibility of the magnetosphere a) Effect of Pd on the magnetopause position Reasonably to assume that the displacements o f the polar cap boundary and of the magnetopause are interrelated. From the equilibrium condition o f the magnetopause - balance of the total pressure P+B2/2no=const, it is easy to see that its compression with increasing pressure Pd rapidly slows down and under values typical for superstorms practically stops. It means that magnetopause nose position has minimal limit. For compressed dipolar field B(r) » 2B(RE) / r 3 to reduce subsolar relative radius L / LQ= rmp/RQ(R0 « 10Re) from 10 to 5 (i.e. half) it is necessary to 6 overcome geomagnetic pressure PnB(r )~ l/r, i.e. to 6 increase Pd in 2 =64 times. Fig. 6 show very slow magnetopause inward motion for Pd/ P BE(r^>10. b) Effect of the southward IMF If we following to Kovner and Feldstein [1972], assume that the southward IMF penetrates by diffusion inside the magnetopause and reduce geomagnetic field, it also results in the dayside magnetopause inward movement to restore the pressure balance (another possible reason is the negative feedback effect of the Region 1 FACs on the BEvalue at the dayside magnetosphere [Maltsev and Lyatsky, 1975; Sibeck et al., 1991; Siscoe et al., 2002]). But it is also easy to see, that the compression o f the magnetosphere decelerates quickly at the amplification of both Pd and negative IMF Bz. Analogical behavior is seen for the polar cap magnetic flux Ч*. Fig. 6 shows that for the powerful superstorm, saturation effect-а growth slowing occurs since values Вг< -30 nT and Pd>10 nPa. 42