Spectral law and polarization properties of the low-frequency waves at themagnetopause

The magnetic fluctuations, at the magnetopause and in the adjacent magnetos heath, exhibit power law spectra which are very reminiscent of turbulent sp ectra. In prospect of future modelizations of such a turbulence, new inform ation is brought about the experimental properties of these fluctuations. T he power laws spectra previously obtained in the ULF range are shown to hol d also in VLF, up to the lower hybrid frequency. Concerning the polarizatio n, I) the direction with respect to the static magnetic field is shown to b e dominantly perpendicular at low frequencies, consistently with Shear Alfv en modes in this range, and 2) no right-hand sense of rotation can be evide nced at frequencies higher than the proton gyrofrequency, although one coul d expect the fast magnetosonic mode to be dominant in this range. The physi cal implications of this last observation for the non linear effects at wor k in the turbulence are briefly discussed.