Comparing various multi-component global heliosphere models

Modeling of the global heliosphere seeks to investigate the interaction of the solar wind with the partially ionized local interstellar medium. Models that treat neutral hydrogen self-consistently and in great detail, together with the plasma, but that neglect magnetic fields, constitute a sub-category within global heliospheric models. There are several different modeling strategies used for this sub-category in the literature. Differences and commonalities in the modeling results from different strategies are pointed out. Plasma-only models and fully self-consistent models from four research groups, for which the neutral species is modeled with either one, three, or four fluids, or else kinetically, are run with the same boundary parameters and equations. They are compared to each other with respect to the locations of key heliospheric boundary locations and with respect to the neutral hydrogen content throughout the heliosphere. In many respects, the models' predictions are similar. In particular, the locations of the termination shock agree to within 7% in the nose direction and to within 14% in the downwind direction. The nose locations of the heliopause agree to within 5%. The filtration of neutral hydrogen from the interstellar medium into the inner heliosphere, however, is model dependent, as are other neutral results including the hydrogen wall. These differences are closely linked to the strength of the interstellar bow shock. The comparison also underlines that it is critical to include neutral hydrogen into global heliospheric models.Comment: 10 pages, 4 figures, submitted to a special section at A&A of an ISSI team "Determination of the physical Hydrogen parameters of the LIC from within the Heliosphere

On the effect of transport coefficient anisotropy on the plasma flow in heliospheric interface

The plasma flow in the heliospheric interface is considered. The applicability of hydrodynamic description for this flow is studied. The effect of the magnetic field on the transport properties in the interface plasma is discussed and the dimensionless parameters related to the plasma flow are estimated. It is found that both resistivity and Hall effect can be neglected in Ohm's law, so that the classical induction equation of the ideal magnetohydrodynamic can be used. The Reynolds number is moderately large, so the approximation of inviscid plasma is fairly good. The most important dissipative process is thermal conduction along the magnetic field lines. This effect has to be definitely taken into account. The results obtained in the paper are used to outline the ways for advancing the existing models of the heliospheric interface

Modeling of the heliospheric interface: multi-component nature of the heliospheric plasma

We present a new model of the heliospheric interface - the region of the solar wind interaction with the local interstellar medium. This new model performs a multi-component treatment of charged particles in the heliosphere. All charged particles are divided into several co-moving types. The coldest type, with parameters typical of original solar wind protons, is considered in the framework of fluid approximation. The hot pickup proton components created from interstellar H atoms and heliospheric ENAs by charge exchange, electron impact ionization and photoionization are treated kinetically. The charged components are considered self-consistently with interstellar H atoms, which are described kinetically as well. To solve the kinetic equation for H atoms we use the Monte Carlo method with splitting of trajectories, which allows us 1) to reduce statistical uncertainties allowing correct interpretation of observational data, 2) to separate all H atoms in the heliosphere into several populations depending on the place of their birth and on the type of parent protons.Comment: A&A accepte

Ionization rates in the heliosheath and in astrosheaths

In the heliosphere, especially in the inner heliosheath, mass-, momentum-, and energy loading induced by the ionization of neutral interstellar species plays an important, but for some species, especially Helium, an underestimated role. We discuss the implementation of charge exchange and electron impact processes for interstellar neutral Hydrogen and Helium and their implications for further modeling. Especially, we emphasize the importance of electron impact and a more sophisticated numerical treatment of the charge exchange reactions. Moreover, we discuss the non-resonant charge exchange effects. The rate coefficients are discussed and the influence of the cross-sections in the (M)HD equations for different reactions are revised as well as their representation in the collision integrals. Electron impact is in some regions of the heliosphere, particularly in the heliotail, more effective than charge exchange, and the ionization of neutral interstellar Helium contributes about 40% to the mass- and momentum loading in the inner heliosheath. The charge exchange cross-sections need to be modeled with higher accuracy, especially in view of the latest developments in their description. The ionization of Helium and electron impact ionization of Hydrogen needs to be taken into account for the modeling of the heliosheath and, in general, astrosheaths. Moreover, the charge exchange cross-sections need to be handled in a more sophisticated way, either by developing better analytic approximations or by solving the collision integrals numerically.Comment: 18 pages, 9 Figure

Distribution of Interstellar Hydrogen Atoms in the Heliosphere and Backscattered Solar Lyman-α

We review the modern concepts of penetration of interstellar atoms of hydrogen into the heliosphere up to 1 AU. Before entering into the heliosphere the atoms penetrate through the region of the solar wind (SW) interaction with the local interstellar medium (LISM). In the interaction region the atoms can exchange charge with both solar wind and interstellar protons disturbed in the SW/LISM interaction region. Charge exchange results in a disturbance of the pristine interstellar atom flow in the interaction region, and, therefore, the parameters of interstellar gas inside the heliosphere are different from their interstellar values. This makes it more difficult to determine local interstellar parameters from measurements of the interstellar atoms inside the heliosphere, but, on the other side, opens possibilities to study the SW/LISM interaction region remotely. This paper overviews the main physical phenomena and modern models of the SW/LISM interaction and presents a state-of-art 3D kinetic model of the interstellar hydrogen gas inside the heliosphere. The distributions of the gas parameters are compared with the distributions obtained in the context of the classical hot model. Quantitative and qualitative differences are discussed. The state-of-art model is employed to calculate spectra of the backscattered Lyman- α radiation as they would be measured at 1 AU and the zero, first and second moments of the spectra. It is shown that the SW/LISM interaction imprints in the spatial and velocity distribution of the interstellar atoms are revealed in the intensities, line-shifts, and line-widths of the distribution functions. A qualitative comparison of the model results with SOHO/SWAN data are presented