Thermodynamics of the Solar Wind Electrons

Abstract:

The temperature gradients are observed to depart from a classical adiabatic expansion for both the protons and the electrons in the Solar Wind. This property is often use to invoke the need for an additional energy source in order to explain these gradients and possibly the Solar Wind acceleration itself.

Is this need really justified? I will review recent observations and literature on this topic and argue that if additional heating energy may be needed for the protons, this statement is less obvious for the solar wind electrons.