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.

Earthward electricfield in the geomagnetic current sheet times in which the length of line AS is increased. It means that E'x = Ex and nonzero Ex can not appear. The further calculation with use of model of CS gives value Ex ~ 1 mV/m in the CS configuration. The authors of (Zelenyi at al., 2010a) conclude that the electric field Ex directed to the Earth obtained in such a way is a hidden one. It can't to influence on the magnetospheric plasma outside the sheet and to create FAC. iZ .................. .......................... __________ % <ri =<p,+(d<p/ds)&s, <ji =<fi1+{Rtplds)hs1 As, - Л ч3 =(3Av/flr)Ar + 8As dtp dx Bs \ N - Ax Fig. 4. Magnetic field lines (broken lines) and potential drops in CS according Zelenyi et al. As the additional mechanism causing increase of the earthward electric field Ex authors (Zelenyi at al., 2010a) consider ion drift to the Earth. For this purpose existence of Ey field component is also introduced, but in this case energy dissipation (Eyxjy> 0) is inconsistence with plasma collisionless, which is necessary for drift approximation. It is confirmed that the ion drift velocity is bigger than the electron drift velocity: Vxi - Vxe = AVX~ p(2V2 (Ey/Bz). However, ions moving forward create the field of polarization directed not to the Earth, but from the Earth. Therefore the account of the fast ion drift will lead to reduction of the field directed to the Earth, or to change of the electric field direction on the opposite. Thus, within the frame of drift approach it is impossible to estimate not only the electric field value, but also field direction. Used in the work (Zelenyi at al., 2010a, b) drift approach is extremely useful to rough estimates of plasma behavior. However, it doesn't consider of several effects which in some problems of plasma physics are basic. It doesn't consider the force of a magnetic tension, to which in the real CS forces of ion inertia and the pressure gradient counteract. In absence of such forces a magnetic configuration must to turn in potential one with the light velocity. In the Zelenyi model only electrons are connected with magnetic field lines (magnetized). It is correct, but it means that force of a magnetic tension is applied to electrons. Forward electron gas motion induces electric charge polarization. Because of plasma polarization the electric field directed to the Earth is created. Thus the Hall effect, which is absent in drift approach, is gracefully described in magnetohydrodynmics by the formula E = jxB/nec. Conclusion Recent measurements show that most of the current in CS is transferred by electron. So the previous conclusion of Zelenyi et al. (2002) about ion role in CS current can not be considered as a reason against Hall effect appearance in the Earth magnetic tail. Application of the drift approximation assumes the conditions of collisionless, i.e. absence of magnetic energy dissipation including heating due to anomalous resistivity in CS. However, in formulating the problem of the drift approximation, the existence of strong temperature gradient across CS is assumed ( Zelenyi at al., 2010a, b). This gradient indicates efficient energy dissipation. Existence of a temperature gradient contradicts to the requirement of the drift approximation applicability. Plasma heating shows magnetic energy dissipation in CS in spite of energy dissipation inconsistent with drift approximation. So, the ideology based on drift approximation that does not take into account the role of solar wind for CS generation is not applicable. The Earthward electric field in drift approximation has been obtained in presence of the electric field normal to the CS, if the electric field projection on the magnetic line is changed at angle inclination of this line, but the length of magnetic line remains constant. These geometric considerations are wrong; the nonzero Earthward electric field never can appear such a way. The earthward electric field in the geomagmetic tail is a result o f plasma polarization due to the F = jxB/c force applied to electrons. This electric field can be responsible for FAC and westward jet creation. Acknowledgments. This work was supported by RFBR grant № 09-02-00043. 55