Hybrid models of solar wind plasma heating

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.

Ion Heating in Inhomogeneous Expanding Solar Wind Plasma: The Role of Parallel and Oblique Ion-Cyclotron Waves

“…As in previous hybrid modeling studies (e.g., Ofman 2010;Ofman et al 2011Ofman et al , 2014, we see that the presence of a superAlfvénic drift leads to magnetosonic instability that affects the ions and to a rapid He ++ ion heating in the perpendicular direction increasing the ion temperature anisotropy. This anisotropy decays quickly due to secondary ion-cyclotron instability resulting in emission of a spectrum of secondary ion-cyclotron waves, which in turn resonate with the protons causing the proton temperature anisotropy to increase following the relaxation of the He ++ temperature anisotropy.…”

“…It is evident from Figure 5 that the slow solar wind expansion rate has little or no effect on the particle energies, while a moderate expansion rate has an increasing effect in the perpendicular component of the ions and a slight decreasing effect on the perpendicular energy of the protons. These results are in agreement with the previous studies of magnetosonic drift instability in inhomogeneous background solar wind plasma (e.g., Ofman 2010;Ofman et al 2011Ofman et al , 2014. The expansion appears to mostly affect the proton temperature anisotropy (since the protons are not heated significantly by the instability) and speeds up the decrease of the relative He ++ -proton drift.…”

“…We refer the reader to Liewer et al (2001), Hellinger et al (2003), Hellinger et al (2005), Ofman et al (2011Ofman et al ( , 2014 and Maneva et al (2013Maneva et al ( , 2014 for further details on the expanding box model and its implementation.…”

“…Several 2D hybrid models of homogeneous solar wind plasma heating by a spectrum of ion cyclotron waves include studies by Gary et al (2001Gary et al ( , 2003Gary et al ( , 2006; Hellinger et al (2003Hellinger et al ( , 2005; Omidi et al (2014); Maneva et al (2014). Previous works that study the effect of the expansion on homogeneous solar wind plasma heated by ion-cyclotron waves with one-dimensional (1D) and twodimensional (2D) hybrid models include Liewer et al (2001); Ofman et al (2011Ofman et al ( , 2014; Maneva et al (2013Maneva et al ( , 2014; Hellinger et al (2013).…”

Kinetic instabilities in the solar wind driven by temperature anisotropies

“…Hybrid simulations of the expanding system were carried out by Hellinger et al (2003), Matteini et al (2006Matteini et al ( , 2012, Trávníček et al (2007), , Camporeale and Burgess (2010), Ofman et al (2011Ofman et al ( , 2014, and Moya et al (2012), which are in many ways equivalent to the macroscopic-kinetic model of the solar wind. Of course, numerical simulations are more rigorous in that they contain full nonlinear physics, but fluid/kinetic model is an efficient way to investigate the large-scale physics and its coupling to small kinetic-scale processes.…”