Transition From Turbulence to Dissipation in the Solar Wind Plasma: Results From Hybrid Simulations

Abstract:

Spacecraft observations such as WIND, and ACE show ample evidence of turbulent spectra of magnetic and velocity fluctuations, and kinetic dissipation in the solar wind plasma at ~1AU. Helios and MESSENGER confirm these properties close to the Sun at ~0.3AU, and future Solar Probe+ mission will provide information on turbulent spectra closer to the Sun in the outer corona. The transition between turbulence and dissipation occurs at scales that have clear dependence on heliocentric distance, as expected from solar wind expansion. We perform 2.5 hybrid modeling studies (where ions are described as particles, and electrons as background fluid) of the evolution of the turbulent spectra of fluctuations in electron-proton-He++ solar wind plasma at 1AU and closer to the Sun by varying the model plasma parameters. We investigate the dependence of the turbulence cascade and the transition to kinetic dissipation on the plasma parameters. We consider the effects of the solar wind expansion on the evolution of the turbulence and on the ion heating. We find important differences between the magnetic fluctuations spectrum, and the velocity fluctuations parallel and perpendicular to the field affected by ion-cyclotron, and mirror instabilities, as well as proton and alpha density fluctuations due to coupling to magnetosonic instability. We investigate the effects of the alpha-proton drift, and an injected spectrum on the turbulent magnetic fluctuations on the evolution of the solar wind plasma and the ion heating.