Kinetic evolution of the perpendicular turbulent cascade in the solar wind

¹ Dipartimento di Fisica and CNISM, Università di Pisa - 56127 Pisa, Italy, EU
² Université de Nice Sophia Antipolis, CNRS, Observatoire de la Côte d'Azur - 06304 Nice Cedex 4, France, EU
³ Dipartimento di Fisica and CNISM, Università della Calabria - 87036 Rende (CS), Italy, EU

^a francesco.valentini@fis.unical.it

Received: 23 September 2010
Accepted: 29 October 2010

Abstract

We investigate the solar-wind dynamics at typical kinetic scales resulting from a turbulent cascade along the direction strictly perpendicular to a background magnetic field. We use a hybrid Vlasov-Maxwell numerical model that solves Vlasov equation for the proton distribution function. Electrons are assumed as an isothermal fluid. We find, over a range of about four decades of wavenumbers, a Kolmogorov slope at wavelengths larger than the proton inertial scale and an abrupt change in the scaling law across the proton inertial length. The energy is carried along the cascade in the form of magneto-sonic fluctuations while the short-scale termination of the spectra is dominated by a significant level of electrostatic activity. As a result of the turbulent energy cascade, we observe the generation of shock structures where the proton distribution function departs from the Maxwellian equilibrium configuration displaying the presence of beams of accelerated protons. Finally, quasi-static magnetic-field structures are produced in the early stage of the system dynamics and remain stable up to the end of the simulation. The numerical results discussed in the present paper qualitatively reproduce a complex phenomenology frequently recovered by spacecraft observations.