The effect of spectral anisotropy of fast magnetosonic turbulence on the plasma heating at the proton kinetic scales

The energy transport associated with the fast magnetosonic turbulence in a low-beta plasma is one of the possible driving forces of the solar wind. We discuss two different kinds of the turbulence spectra: a unidirectional spectrum of fluctuations propagating away from the Sun and a bidirectional spectrum composed of sunward and antisunward modes. The evolution of the system is analyzed with the help of hybrid numerical simulations at the proton kinetic scales. It is shown that, in the unidirectional case, the heating is always preferentially across the background magnetic field. It is this property that allows the solar wind plasma to be propelled away from the Sun by the mirror force of the inhomogeneous magnetic field. Adding the counter-propagating modes reverses the sense of the energy deposition with the parallel heating now dominating the process. However, the parallel heating is produced mostly by fast modes propagating along the magnetic field. If these modes are eliminated, the heating becomes perpendicular again.