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.

The saturation effect o f the Poyntingflux into the magnetosphere during superstorms Thus, even for stronger superstorm SW parameters, it is practically impossible to compress the magnetosphere more than twice. That is why there must be an upper limit of the magnetic flux transfer into the polar cap. The MHD model calculations for steady conditions made for the Bz values from B2= -5 nT to Bz= -20 nT, gave a permanent Lmp decrease and Qd growth with no signs of a saturation. This is contrary to the actual observed saturation of Upc and T [e.g. Lopez et al., 2007; Borovsky et al., 2009]. 0.4- dipole model a 10 20 30 40 Pd/ P ec PPMRL model h Nov 2003 Superstorm 20 i j ] ‘ 5 . т у Г I I l '" l 1V —| T— I " I 10 15 Pd. nPa PPMRL _ Superstorm 20.11.2003 u -1UL, --------,------------i----------- r>-----=— ------ 0 -20 -40 Bz, nT Figure 6. (a) Dipole model: the relative subsolar magnetopause distance as a function of the relative SW pressure Pd/ PBE(r0) changing from 1 up to value 26, when L/L0=l/2. (b, c) MHD model: Lmp as a function of Pd (b) and B2 (c) during the superstorm. Solid line- approximating curve. Possible reasons for this are rather long period (several hours) required to meet the steady condition, that for the actual conditions during superstorms is not realized; and that the real saturation level is below Bzmin=-20 nT and was not achieved. Conclusions Comparison of variations of the Poynting flux into the magnetosphere obtained by MIT and the MHD model for the 20 November 2003 event, has shown: - In the initial phase of the storm, when the Pd and southward IMF values were small (Pd <4 nPa, Bz < -5 nT), input power values were almost the same; - With the increasing of Pdand southward IMF, there is a growth of the Poynting flux. This growth begins to slow down when Pd ~ (5-8), and when Pd> 14 nPa it stops; the Poynting flux increase depending on the southward IMF slows down when B2 < -20nT and almost stops at Bz < -40nT, rarely observed for superstorms, while about half of the power transferred into the magnetosphere gets into the polar cap (e' ~ 0.5 Qehn). We assume that the saturation effect of the and Poynting fluxes are associated with the slowing of both the magnetosphere compression and the polar cap expansion at significant SW strengthening. The PPMLR-MHD model shows the saturation effect for superstorm conditions, but does not show it in steady conditions for Bz > -20nT. Acknowledgments. The AE index was obtained through the WDC Website, Kyoto, magnetic data from the CANOPUS, INTERMAGNET, GIMA, MACCS, IMAGE and SuperDARN international projects, from magnetic networks in Arctic and the Antarctic (the Shafer Institute of Cosmo-Physical Research and Aeronomy SBRAS, Arctic and Antarctic Research Institute, and DMI), and individual magnetic observatories. Study is supported by RFBR Grants 14- 05-91165 and 15-05-05561, C. Wang is supported by the NSFC grant 413111039 References Borovsky J.E., B. Lavraud and M. Kuznetsova. Polar cap potential saturation, dayside reconnection, and changes to the magnetosphere// J. Geophys. Res. 114. A03224, doi:10.1029/2009JA014058. 2009 Gao Y., M.G. Kivelson, and R.J. Walker. Two models of cross polar cap potential saturation compared: Siscoe - Hill model versus Kivelson-Ridley model// J. Geophys. Res. 118. 794-803. doi:10.1002/jgra.50124. 2013 Hu Y.Q., Z. Peng, C. Wang, and J. R. Kan. 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