KINETIC TURBULENCE IN THE TERRESTRIAL MAGNETOSHEATH: CLUSTER OBSERVATIONS

We present a first statistical study of subproton- and electron-scale turbulence in the terrestrial magnetosheath using waveform data measured by the Cluster/STAFF search coil magnetometer in the frequency range [1, 180] Hz. It is found that clear spectral breaks exist near the electron scale, which separate two power-law-like frequency bands referred to as the dispersive and the electron dissipation ranges. The frequencies of the breaks f sub(b) are shown to be well correlated with the electron gyroscale [rho] sub(e) rather than with the electron inertial length d sub(e). The distribution of the slopes below f sub(b) is found to be narrow and peaks near -2.9, while that of the slopes above f sub(b) is found to be broader, peaking near -5.2, with values as low as -7.5. This is the first time that such steep power-law spectra are reported in space plasma turbulence. These observations provide new constraints on theoretical modeling of kinetic turbulence and dissipation in collisionless magnetized plasmas.