The effects of inhomogeneous proton‐α drifts on the heating of the solar wind

Abstract

AbstractPrevious modeling studies have demonstrated that waves and super‐Alfvénic drift can lead to perpendicular preferential heating of the α particles with respect to protons. Using 2.5‐D hybrid model of the solar wind α‐proton plasma, we study the effects of inhomogeneous (across the magnetic field) background streaming focusing on the fast solar wind. We explore the effects of an initial relative, inhomogeneous ion drift on the perpendicular ion heating and cooling and consider the effects of solar wind expansion. We study the spectrum of the magnetic fluctuations in the inhomogeneous background solar wind and demonstrate the generation of oblique waves and their effects on enhanced resonant anisotropic ion heating. The model reproduces the typical ion temperature anisotropy values seen in observations. Using our model, we find that inhomogeneous super‐Alfvénic ion drift in the plasma generates significant power of oblique waves in the solar wind plasma, in addition to enhanced heating compared to the nondrifting populations. We demonstrate the effects of various inhomogeneity profiles and regions of the drift on the ion anisotropic heating in super‐Alfvénic and near‐Alfvénic drifts. We find that the cooling effect due to the solar wind expansion is not significant when super‐Alfvénic drifts are considered.