Alfvén wave propagation and ion cyclotron interactions in the expanding solar wind: One‐dimensional hybrid simulations

Abstract

Abstract. We carry out one-dimensional hybrid simulations of Alfv•n waves propagating along the magnetic field in the presence of a mean radial spherically expanding plasma outflow, representing fast solar wind streams. The equations for particle ions of multiple species and fluid electrons are solved using the Expanding Box Model, a locally Cartesian representation of motion in spherical coordinates, in a frame moving with the local average wind speed. The model gives a minimally consistent description of the effects associated with such motion on particle dynamics, e.g., the flux-conserving decrease of magnetic field intensity and consequent decrease of cyclotron frequency with increasing distance from the Sun. The cyclotron frequency decreases faster than Alfv•n wave frequency, allowing fluctuations below the cyclotron frequency at smaller distance from the Sun to come into cyclotron resonance at greater distances. The hybrid treatment yields a fully self-consistent description of the consequent cyclotron wave-particle interaction in a multi-ion plasma. We present results for cases of monochromatic circularly polarized Alfv•n waves propagating radially outward and for initially well developed Alfv•nic spectra with and without alpha particles. When both alpha particles and protons are present, the alpha particles, which come into resonance first as the wind expands, are observed to be preferentially heated and accelerated. For high beta (equal to ratio of ion pressure to magnetic field pressure) the amount of alpha particles acceleration and heating is limited by the available wave power. For low beta cases the amount of heating and acceleration is limited, not by the wave power, but by the depletion of the distribution function in the resonance region by pitch-angle scattering. The implication of these results for solar wind models is discussed.

Hybrid models of solar wind plasma heating

“…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, , 2003Ofman et al, 2001Ofman et al, , 2002Ofman et al, , 2005Xie et al, 2004;Ofman and Viñas, 2007;Ofman, 2010a). The effects of solar wind expansion of the evolution of the wave-particles interactions and on the heating was also studied (Liewer et al, 2001;Hellinger et al, 2003Hellinger et al, , 2005Hellinger and Trávníček, 2008).…”

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

“…The expansion model used was initially proposed for MHD equations by Grappin & Velli (1996) and was later implemented to hybrid 1D and 2D models (Liewer et al 2001;Hellinger et al 2003). Our version of the model has been implemented in previous studies of solar wind expansion in 1D hybrid modeling with two ion species (Ofman et al 2011;Maneva et al 2013) and in a 2D hybrid model of homogenous H + -He ++ solar wind plasma Maneva et al 2014).…”

“…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).…”

Comparison of the effects of wave-particle interactions and the kinetic suprathermal electron population on the acceleration of the solar wind

“…Wave-particle interactions have been considered as a possible solar wind heating mechanism, and their effects have been studied by a number of authors (e.g. Hollweg & Turner 1978;Dusenbery & Hollweg 1981;Marsch et al 1982c;Isenberg 1984;Leer et al 1992;Hu et al 1997;Czechowski et al 1998;Cranmer et al 1999b;Hu & Habbal 1999;Li et al 1999;Tam & Chang 1999a;Isenberg et al 2000;Cranmer 2001;Gary et al 2001;Liewer et al 2001;Tam & Chang 2001;Tu & Marsch 2001;Vocks & Marsch 2001). Experimentally, there has been increasing evidence suggesting that wave-particle interactions play a significant role in the evolution and acceleration of the solar wind.…”