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.

The depletion and dipolarization o fthe magneticflux tubes above auroral arc t t ADIABATIC PROCESS / I 4 v 0 .0 5 2 3 .4 2 3 .6 2 3 .8 rt COLATITUDE 0° Fig.3 r(RE) Fig.4 Fig.5 It is seen in fig.3 that the thermal energy of charged particles decreases significantly after dipolarization. The figure also shows the value of the thermal energy of particles in flux tubes in the case of the adiabatic process. The noticeable increase in the thermal energy with decreasing colatitude в is associated with the significant change of the magnetic flux tubes volume at large distances from the Earth in the magnetotail during dipolarization. The decrease of the magnetic flux tubes volume during the adiabatic process is produced by the work of external forces namely the operation of the electric field. The electric field in this case is solenodial and is caused by the increase of the magnetic field. Considering the time dipolarization equal to 5 minutes we can estimate the plasma velocity at different distances from the Earth using the displacement of the magnetic field lines. Fig.4 shows the variation of the magnetic field lines before and after dipolarization (- - before depolarization, - after) calculated with the magnetic field model [Tsyganenko, 1995]. Fig5. shows the change in the velocity of the magnetic field lines and plasma velocity vers, the distance from the Earth. The reducing the plasma velocity toward the Earth during dipolarization is a well established experimental fact. The velocities values obtained from the calculations coincide with observations also [Baumjohann et al., 1990; Angelopoulos et al 1994; Reeves et al., 1996, Shiokawa et al., 1997]. Estimation of magnetic flux tubes cooling Let us appreciate cooling of the magnetic field tubes due to the precipitation of the particles. The current in the arcs of the aurora can reach values of 10 A/km2, the average energy of injected particles will be taken as 5 keV. The time of depolarization is 5 minutes. Then the amount of heat lost by a magnetic tube with a single magnetic flux is equal to 0.05 R e (J/ Wb). These losses should be added to the flow of the electromagnetic energy into the ionosphere, it can be estimated by the Joule losses in the auroral arc. Taking the electric field across the arc equal to 20 mV/ m and the integrated Pedersen conductivity of the ionosphere in the auroral arc equal to 40 Cm [Marklund et al., 1982] we receive losses 0.015 RE (J / Wb) and total losses equal to 0.065 RE {J I Wb). This value is sufficient to explain the cooling of the magnetic flux tubes at distances of up to 10 RE. At large distances the volume of the magnetic flux 23