Experimental study of the plasma acceleration/heating by large-amplitude Alfven waves in the space

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Alfven waves were found to propagate toward the earth in the nightside magnetosphere. They are considered to be associated with the auroral activity at the ionospheric altitudes. We have investigated the electric and magnetic field variations measured by Geotail in the mid-tail region, 10-30 Re. We found large-amplitude electric field fluctuations and the corresponding magnetic field fluctuations having the components in the direction perpendicular to the ambient magnetic field. These fluctuations were identified as Alfven waves from the ratio between the amplitudes of electric and magnetic field. These large-amplitude Alfven waves often propagate in the direction coincides with the plasma flow, and earthward at the same time. We will further select events in which the fluctuations are identified as waves definitely. We will report the statistical result about the correspondence with the plasma properties and estimation of the energy flux carried by the Alfven waves.