Reflection Driven MHD Turbulence in the Solar Atmosphere and Wind

Alfv,nic turbulence is usually invoked and used in many solar wind models (Isenberg and Hollweg, 1982, J. Geophys. Res. 87:5023; Tu et al. 1984, J. Geophys. Res. 89:9695; Hu et al. 2000, J. Geophys. Res. 105:5093; Li 2003, Astron. Astrphys. 406:345; Isenberg 2004, J. Geophys. Res. 109:3101) as a process responsible for the transfer of energy, released at large scale in the photosphere, towards small scale in the corona, where it is dissipated. Usually an initial spectrum is prescribed since the closest constraint to the spectrum is given by Helios measurements at 0.3 AU. With this work we intend to study the efficiency of the reflection as a driver for the nonlinear interactions of Alfv,n waves, the development of a turbulent spectrum and its evolution in the highly stratified solar atmosphere inside coronal holes. Our main finding is that the perpendicular spectral slope changes substantially at the transition region because of the steep density gradient. As a result a strong turbulent heating occurs, just above the transition region, as requested by current solar wind models.