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.

Magnetospheric storms and substorms, nature and topology o f high latitude current systems ( 1 <32Ф 1 d ( 1 ЗФ j | [ r-cos# dr2 r3 е е д в ) \ - 4 - tzw -cos#—— дФ where Ф = r •cos#• A , Av is the azimuthal component of the vector potential of the magnetic field (B=rofA) in the spherical system of coordinates (г,в, <p). The initial magnetic field not distorted by currents flowing in the plasma is considered the dipole field. Distribution of plasma pressure during the main phase of the magnetic storm is very asymmetric with maximum near midnight and evening. Plasma pressure is near to isotropic during the magnetic storm (see Greenspan and Hamilton [2000]). That is why to analyze the symmetric part of the ring current it is necessary to use p(r) measured during daytime or dawn hours. The obtaining of p(r) requires the crossings of the region of radial plasma pressure gradient for the time, which is much smaller than the time of pressure changes. It is quite difficult using high orbiting satellites. For example, AMPTE CCE passes through the ring current required 3 hours (see Greenspan and Hamilton [2000]). That is why the analysis can be based only on rather random observations for comparatively large magnetic storms. We analyze the pressure profiles published by Hamilton et al. [1988] for great magnetic storm of February' 1986, Williams and Sugiura [1985] and Krimigis et al. [1985] for the magnetic storm of September 4-7, 1984, and Greenspan and Hamilton [2000] for the magnetic storm November 30, 1988. Fig. 4a,b,с shows the comparison of measured Dst with the results of calculations. Calculated Dst was multiplied on the coefficient of 3/2 related to induction currents in the Earth. Fig. 4 demonstrates comparatively good coincidence of the results of calculations and measured Dst in spite of the rather simple used model. Comparatively good coincidence of measured and calculated Dst for the great magnetic storm February 1986 is connected with the position of pressure maxima at comparatively small L where the distortions of the magnetic field by currents in plasma are not very large. It is necessary to mentioned that the discussion of the contribution of tail current in the Dst started with the analysis of this storm when the contribution of Earth currents to Dst was not included (see Greenspan and Hamilton [2000], Feldstein [1992]). Greenspan and Hamilton [2000] tested the DPS relation during maximum phase of 80 magnetic storms and found the strong linear correlation between ring current energy estimated from nightside ion measurements and the Dst index. In contrast, dayside measurements of the ring current energy do not yield a robust correlation with Dst. It seems to us that this result is mainly connected with large distortion of daytime flux tubes and limiting of ring current energy calculations at geocentric distances smaller than 1RE. Taking into account the existence of the high latitude part of the plasma pressure at geocentric distances >7 RE it may be possible to restore the whole pressure profile using data of low orbiting satellites as it was done, for example, by Stepanova et al. [2008]. It is possible to mention also that the introduction of CRC removes the difficulties connected with Iyemori and Rao [1996] effect as near Earth part of tail current becomes the part of the whole ring current. a U T b UT с Fig. 4. The results of the comparison of the value of measured (thick line) and calculated Dst (crosses) for three magnetic storms (a) February 1986, (b) September 4 -7 , 1984, (c) November 30, 1988. Parts of the figures show satellite orbit positions. The produced analysis demonstrates the possibility to restore the traditional interpretation of Dst as mainly the result of ring current (including CRC) development. It is necessary to stress that the suggestion about great role of tail current in Dst formation mitts with definite difficulties discussed by Antonova [2001]. Partial ring current must be localized in the same region near midnight as the tail current, which leads to difficulties 13