Heating the Solar Wind by a Magnetohydrodynamic Turbulent Energy Cascade

Solar wind plasma is known to cool down more slowly while it is blown away from the Sun than expected from an adiabatic spherical expansion. Some source of heating is thus needed to explain the observed temperature radial profile. The presence of a nonlinear turbulent magnetohydrodynamic energy cascade has been recently observed in solar wind plasma. This provides for the first time a direct estimation of the turbulent energy transfer rate, which can contribute to the in situ heating of the wind. The value of such contribution is shown to represent an important fraction (from 5% to 100%) of the total heating, and is strongly correlated with the wind temperature.