Description
(Text)
Nonthermal ion velocity distribution functions are ubiquitous in the fast solar wind, which is permeated by large-amplitude Alfvén waves and plasma wave turbulence, including ion-cyclotron waves. Remote sensing of the solar corona by means of ultraviolet spectroscopy and modeling of in situ measured data indicate that similar anisotropic kinetic ion features are present also in the solar atmosphere, especially in coronal holes where Alfvén waves are considered to be important. In the present work we have investigated the role of parametric instabilities and the consequent wave-particle interactions of parallel monochromatic nonlinear Alfvén-cyclotron waves with solar wind ions as a possible source for the anisotropic preferential ion heating and differential acceleration, as observed both in coronal holes and the fast solar wind. After the onset of parametric instabilities, particles are trapped in the potential well of daughter ion-acoustic waves, whose Landau damping results inparallel ion heating and differential acceleration. Simultaneously, ion beams are formed and nonlinear pitch-angle scattering leads to particle heating transverse to the direction of the background magnetic field. The ion beams are found to be rather persistent and long lived. Simultaneously, the minor ions are differentially accelerated and preferentially heated up to a more than mass proportional temperature ratio, as observed in situ in the fast solar wind. Heavy ions exhibit preferential and anisotropic heating as well, and their differential acceleration is investigated.
(Extract)
There are different ways to detect the presence of electromagnetic waves in the corona and the solar wind. Since we have no direct access to the solar corona, we can infer information about the wave propagation there only by means of remote sensing. One can use photometry by space-born or ground-based telescopes to follow the plasma motion of different solar structures, like coronal loops, prominences or spicules, and deduce the phase speed of the waves. One can also utilize spectroscopy to invert the wave properties, assuming a certain atmospheric model. Both ways are however limited by the resolution of the CCD cameras and hence can only work for relatively low-frequency MHD type waves (ways below any ion-cyclotron gyration). On the contrary, due to the very low density in the solar wind, in order to detect waves activity we rely on in situ measurements with wave-analyzers on board of space-shuttles.
