A Role for Stochastic Heating in the Near-Sun Environment

Abstract:

Determining the mechanisms that heat the solar corona and accelerate the solar wind has been a goal of the heliophysics community since Parker's proposal of the existence of the solar wind. The upcoming Solar Probe Plus and Solar Orbiter missions will help to address this goal through in-situ measurements of the near-Sun environment. In preparation for these missions, we model one proposed mechanism, stochastic ion heating, through numerical evaluation of the gyroaveraged kinetic equation with an added stochastic diffusion term. In particular, we focus on constructing radial profiles of temperature and heating rates as well as the evolution of the proton velocity distribution. Using a fast solar wind model for magnetic and velocity magnitudes, we find that stochastic heating is able to produce temperatures comparable to previous observations, implying that it may be a mechanism that indeed heats the corona and near-Sun solar wind. The proton velocity distributions are shown to significantly deviate from a Maxwellian equilibrium. The core is flattened, while the tails are steepened when compared to a Maxwellian fit to the distribution. To test for stochastic heating in the solar wind, the model distributions are compared to Helios observations from 60 Solar radii, and should be compared to observations from Solar Probe Plus and Solar Orbiter once they become available.