Turbulence et dissipation à petite échelle dans le vent solaire

International audienceTurbulence at MagnetoHydroDynamics (MHD) scales of the solar wind has been studied for more than three decades, using data analyzes, theoretical and numerical modeling. However smaller scales have not been explored until very recently. Here, we review recent results on the first observation of cascade and dissipation of the solar wind turbulence at the electron scales. Thanks to the high resolution magnetic and electric field data of the Cluster spacecraft, we computed the spectra of turbulence up to 100 Hz (in the spaceraft reference frame) and found evidence of energy dissipation around the Doppler-shifted electron gyroscale fe . Before its dissipation, the energy is shown to undergo two cascades: a Kolmogorov-like cascade with a scaling f−1.6 above the proton gyroscale, and a new f−2.3 cascade at the sub-proton and electron gyroscales. Above fe the spectrum has a steeper power law f−4.1 down to the noise level of the instrument. Solving numerically the linear Maxwell-Vlasov equations combined with recent theoretical predictions of the Gyro-Kinetic theory, we show that the present results are consistent with a scenario of a quasi-two-dimensional cascade into Kinetic Alfv´en modes (KAW). New analyses of other data sets, where the Cluster separation ( 100 km) allowed us to explore the sub-proton scales using the k-filtering technique, and to confirm the 2-D nature of the turbulence at those scales