SPRG Seminars
March 12, 2013:
"Proton energetics in the solar wind: Helios reloaded"
Petr Hellinger, Astronomical Institute, AS CR, Prague, Czech Republic
Proton thermal energetics in the solar wind is investigated. Helios observations indicate that protons need to be heated in the perpendicular direction with respect the ambient magnetic field from 0.3 to 1 AU. In the parallel direction protons need to be cooled at 0.3 AU with a cooling rate comparable to the corresponding perpendicular heating rate; between 0.3 and 1 AU the required cooling rate decreases until a transition to heating occurs: by 1 AU the protons require parallel heating, with a heating rate comparable to that required to sustain the perpendicular temperature. The parallel cooling is related to the evolution of the beam-core structure of the proton velocity distribution function, namely to deceleration of the beam with respect to the core. Estimated heating and cooling rates are compared with the turbulent energy cascade rate and with the results of numerical simulations of the proton beam-core system in the expanding solar wind.