THE EIGENMODE OF SOLITARY KINETIC ALFVEN WAVES OBSERVED BY FREJA SATELLITE

The properties of the solitary kinetic Alfven waves (SKAWs) observed b y Freja satellite are studied statistically for a typical event on Mar ch 7, 1994. The eigenmode of the SKAWs observed is still recognized by their anisotropic structure (1000 km x 1 km), their waveform which is similar to that of a wave packet and their frequency close to the loc al oxygen ion cyclotron frequency. If these, spatial structures really exist, they may have resulted from the evolution of the SKAWs or some envelope solitons of ion cyclotron and magnetosonic waves, which is s upported by four statistical results: (1) The phase velocity is direct ly proportional to the Alfven velocity. (2) The amplitudes of the elec tric filed, magnetic field and density fluctuations are directly propo rtional to the timescales of the pulsations. (3) The amplitudes as wel l as the timescales are directly proportional to the phase velocity. ( 4) The polarization sense is both of right circular and left circular mode with different phase relation among the electric field, magnetic field, and density fluctuations. Moreover, the SKAWs are often superpo sed by a strong electrostatic fluctuations at several hundred hertz, t he causal relation between the SKAWs and superposed waves is still unk nown.