Abstract
Abstract. Remote sensing and in-situ observations show that solar wind ions are often hotter than electrons, and the heavy ions flow faster than the protons by up to an Alfvén speed. Turbulent spectrum of Alfvénic fluctuations and shocks were detected in solar wind plasma. Cross-field inhomogeneities in the corona were observed to extend to several tens of solar radii from the Sun. The acceleration and heating of solar wind plasma is studied via 1-D and 2-D hybrid simulations. The models describe the kinetics of protons and heavy ions, and electrons are treated as neutralizing fluid.The expansion of the solar wind is considered in 1-D hybrid model. A spectrum of Alfvénic fluctuations is injected at the computational boundary, produced by differential streaming instability, or initial ion temperature anisotropy, and the parametric dependence of the perpendicular heating of H+-He++ solar wind plasma is studied. It is found that He++ ions are heated efficiently by the Alfvénic wave spectrum below the proton gyroperiod.
Highlights
The solar wind plasma plays a major role in the physical connection between the Sun and the Earth
The heating of the solar wind plasma by Alfvenic fluctuations spectrum is investigated with 1-D and 2-D hybrid models
In previous studies it was shown that inhomogeneity leads to more efficient plasma heating compared to the homogeneous case due to refraction of the input Alfven waves in the inhomogeneous layer and formation of small scales, facilitating more efficient heating than in the homogeneous case
Summary
Hybrid simulations allow relaxing many approximations used in the fluid, multi-fluid, and in linear or quasi-linear kinetic theory and can represent more completely and selfconsistently the wave-particle interactions in the multi-ion solar wind magnetized plasma than previous analytical models These models have been used successfully to study the nonlinear interactions between a spectrum of waves, beams, and ions in solar wind plasma and the resulting anisotropic heating (Gary et al, 2001, 2003; Ofman et al, 2001, 2002, 2005; Xie et al, 2004; Ofman and Vinas, 2007; Ofman, 2010a). The results of that study were motivated by future Solar Probe+ mission that will investigate solar wind proton and He++ components near the Sun at about 10 solar radii (McComas et al, 2008) In this region the solar wind plasma density is inhomogeneous due to quasi-steady structures (compared to kinetic time scales) as evident from SOHO/LASCO observations (e.g., DeForest et al, 2001). We describe some recent results of 2-D hybrid models of inhomogeneous solar wind plasma heated by a spectrum of resonant waves, and the results of 1-D hybrid model that considers the effect of expansion on the evolution of the plasma temperature anisotropy and the p-He++ relative drift
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