SOLAR WIND TURBULENT SPECTRUM AT PLASMA KINETIC SCALES

The description of the turbulent spectrum of magnetic fluctuations in the solar wind in the kinetic range of scales is not yet completely established. Here, we perform a statistical study of 100 spectra measured by the STAFF instrument on the Cluster mission, which allows us to resolve turbulent fluctuations from ion scales down to a fraction of electron scales, i.e., from similar to 10(2) km to similar to 300 m. We show that for k(perpendicular to rho e) epsilon [0.03, 3] (which corresponds approximately to the frequency in the spacecraft frame f epsilon left perpendicular3, 300right perpendicular Hz), all the observed spectra can be described by a general law E(k(perpendicular to)) proportional to k(perpendicular to)(-8/3) exp (-k(perpendicular to rho e)), where k(perpendicular to) is the wavevector component normal to the background magnetic field and rho(e) the electron Larmor radius. This exponential tail found in the solar wind seems compatible with the Landau damping of magnetic fluctuations onto electrons.