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.

“Physics o f Auroral Phenom ena", Proc. XXXIV Annual Seminar, A patity, pp. 5 1 - 5 6 2011 Polar © Kola Science Centre, Russian Academy of Science, 2011 \PZfl4 p e°Physical W J Institute EARTHWARD ELECTRIC FIELD IN THE GEOMAGNETIC CURRENT SHEET I.M. Podgomy1, and A.I. Podgomy2 ‘institutefo r Astronomy RAS, Moscow, Russia, 2Lebedev Physical Institute RAS, Moscow, Russia Abstract. Measurements with the space craft IKB-1300 have shown that the generator of field-aligned currents is located in the geomagnetic tail. The field-aligned currents are generated by the earthward electric field in the magnetotail current sheet (CS). Two-fluid MHD analysis of plasma behavior in CS explains the electric field generation by the Hall effect. The recent space measurements demonstrate that the most current in CS is transferred by electrons. As a result the jxB/c accelerates electrons and the charges polarization generates the earthward electric field. Connection of the pair of field-aligned currents (FAC) occurs in the ionosphere, and the westward electrojet is located between FAC pair. The current in CS is generated in the interface between plasma of the solar wind and the tail magnetic field. The attempt to explain current generation in CS by the drift of particles in electric and magnetic fields of the tail, which origin isn't connected with the solar wind can't be justified. Using the drift approximation some authors claimed that the current in the current sheet is carried by ions. This conclusion is erroneous. At drift approach the magnetic configuration represents the closed system which is independent of the solar wind, and the stationary electric field exists due to the temperature gradient across a tail. The temperature gradient appears as a result of energy dissipation in CS. The existence of such temperature gradient contradicts the assumption about collisionless conditions. Introduction The geomagnetic tail is responsible for the most important energetic phenomena observed in the Earth magnetosphere, such as plasma injection from CS and aurora production. The creation of the radiation belt due to fast particles injection from the magnetic tail has been demonstrated in the laboratory simulation [Dubinin and Podgomy, 1974]. The geomagnetic tail is formed due to interaction of the solar wind with the field of the Earth. The plasma flow (solar wind) extending lines of the magnetic field. An electric generator that produced the current in CS is situated in interface between solar wind and the Earth magnetic field. The role of the CS electric field in the magnetosphere dynamics is still under discussion. The technical problems do not permit to get reliable results of electric field vector measurements in geomagnetic CS. The aim of this paper is to consider up to date situation. The current generated in each of the tail lobes is closed in CS separating opposite directed magnetic lines. Two independent closed electrical circuits are formed as shown in Fig. la. These currents can be overlapped in CS, and the current distribution with one maximum is observed in the central plane as shown in Figure lb. Conditions of overlapping currents Ij and I2 are difficult to formulate. Results obtained by Isralevich at al. [2008] show that two current maxima are observed at strong current, i. e. at big magnetic fluxes in the tail. Two different current 7 7 generators A Z. Л * - Boundary layer ’ SW "sw Boundary layer (current generator) (current generator) Fig. 1. Two different models of the electric circuit system in the geomagnetic tail. CS is a dissipative element of the electric circuit. The strong temperature gradient across the sheet (Teш ~ 1 keV) and earthward plasma ejection demonstrate fast magnetic energy dissipation. An important feature of CS is the existence of a normal magnetic field component. CS isn't a neutral one. The force of a magnetic tension can be 51