ИСТИНА

In this presentation we consider the correlation between an electron temperature anisotropy in the Earth's magnetotail and an dawn-dusk component of the magnetic eld By. We use nine years of Cluster measurements of parallel (pitch-angles are [����15; 15]) and perpendicular (pitch-angles are[75; 105]) electron phase space densities in the middle tail. We show that the large values of By component corresponds to the dominance of the parallel phase space density for energies larger than 50 eV. The maximum of the ratio of parallel and perpendicular space densities increases signicantly for the interval By in (0; 10) nT. T We separate the dependencies of the electron anisotropy on Bz and on By components of magnetic eld: there is a strong increase of phase space density ratio with the increase of By=Bz ratio. We analyse several events with strongest electron anisotropy observed at X 2 [-16;-18]: ratio of phase space density varies signicantly within one-two minute time interval. Thus, we suggest that the main source of the electron temperature anisotropy corresponds to short transient processes in the magnetotail region.