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The latitudinal velocity component. The solar distance is given in AU ( x − axis), the latitude in degrees ( y − axis), and the speed is colour-coded. For details see text.
Source publication
It has been found that pick-up ions at their dynamical incorporation into the solar wind modify the original conditions of the asymptotic solar wind plasma flow. In this respect, it has meanwhile been revealed in many papers that these type of solar wind modifications, i.e. deceleration and decrease of effective Mach number, are not only due to the...
Contexts in source publication
Context 1
... 4. The ratio of density perturbation and the undisturbed density: δρ/ρ 0 . The labels are analogous to that of Fig. 2, except for the colour-code, which now gives the ratio of the density perturbation and the undisturbed density.
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Context 2
... M A denotes the Alfvén Mach number of the solar wind flow and ξ is again the relative abundance of pick-up ions with respect to solar wind protons. Inserting now concrete numbers for the above quantities at r ≥ 20 AU one may be convinced that δP ≤ ( 1 / 20 ) . This expresses the fact that latitudinal magnetic pressures, though acting opposite to the pick-up ion pressures, do not change the results presented in the section before. In the preceding sections of this paper we have developed a theoretical description of the three-dimensional solar wind outflow under the action of radial and latitudinal pick-up ion pressure gradients. In this paper we started out from the typical solar wind flow configuration which was found for typical solar minimum conditions during the first and second polar latitude passage of the ULYSSES space probe (see McComas et al., 2000). As a consequence of the strong latitude gradients in the radial solar wind velocity and density, associated latitudinal pick-up ion pressure gradients can be derived which induce nonnegligible latitudinal solar wind velocity components. As a consequence of the induced non-radial solar wind flow configurations, complicated structures of perturbed solar wind density and velocity components arise. In Figs. 2 through 4 iso-contours of these perturbations are shown, which can be taken as a visual aid for the interpre- tation of plasma measurements of distant heliospheric space probes, such as VOYAGER-1/2 or PIONEER-10/11 (see, e.g. Whang, 1998; Wang et al., 2000; Richardson et al., 2003). In Fig. 2 one can see the 2-dimensional distribution of latitudinal solar wind speeds as a function of solar distance r in [AU] and of latitude θ . At small distance r < 10 AU nearly no latitudinal velocity is found. Also at ecliptic latitudes θ < 7 ◦ and at polar latitudes θ > 50 ◦ no latitudinal velocities are developing, even up to large distances. At intermediate latitudes 10 ◦ < θ < 45 ◦ , however, astonishingly ...
Citations
... In order to compare our above result for power law PUI pressures with earlier work (Fahr and Fichtner, 1995;Fahr and Rucinski, 1999;Fahr and Scherer, 2004) we can represent the above result in the following form ...
We study the phasespace behaviour of heliospheric pick-up ions after the time of their injection as newly created ions into the solar wind bulk flow from either charge exchange or photoionization of interplanetary neutral atoms. As interaction with the ambient MHD wave fields we allow for rapid pitch angle diffusion, but for the beginning of this paper we shall neglect the effect of quasilinear or nonlinear energy diffusion (Fermi-2 acceleration) induced by counterflowing ambient waves. In the up-to-now literature connected with the convection of pick-up ions by the solar wind only adiabatic cooling of these ions is considered which in the solar wind frame takes care of filling the gap between the injection energy and energies of the thermal bulk of solar wind ions. Here we reinvestigate the basics of the theory behind this assumption of adiabatic pick-up ion reactions and correlated predictions derived from it. We then compare it with the new assumption of a pure magnetic cooling of pick-up ions simply resulting from their being convected in an interplanetary magnetic field which decreases in magnitude with increase of solar distance. We compare the results for pick-up ion distribution functions derived along both ways and can point out essential differences of observational and diagnostic relevance. Furthermore we then include stochastic acceleration processes by wave-particle interactions. As we can show, magnetic cooling in conjunction with diffusive acceleration by wave-particle interaction allows for an unbroken power law with the unique power index γ=−5 beginning from lowest velocities up to highest energy particles of about 100 KeV which just marginally can be in resonance with magnetoacoustic turbulences. Consequences for the resulting pick-up ion pressures are also analysed.
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.
To study the effects of interstellar pickup protons and turbulence on the structure and dynamics of the solar wind, we have developed a fully three-dimensional magnetohydrodynamic solar wind model that treats interstellar pickup protons as a separate fluid and incorporates the transport of turbulence and turbulent heating. The governing system of equations combines the mean-field equations for the solar wind plasma, magnetic field, and pickup protons and the turbulence transport equations for the turbulent energy, normalized cross-helicity, and correlation length. The model equations account for photoionization of interstellar hydrogen atoms and their charge exchange with solar wind protons, energy transfer from pickup protons to solar wind protons, and plasma heating by turbulent dissipation. Separate mass and energy equations are used for the solar wind and pickup protons, though a single momentum equation is employed under the assumption that the pickup protons are comoving with the solar wind protons. We compute the global structure of the solar wind plasma, magnetic field, and turbulence in the region from 0.3 to 100 AU for a source magnetic dipole on the Sun tilted by 0 Degree-Sign -90 Degree-Sign and compare our results with Voyager 2 observations. The results computed with and without pickup protons are superposed to evaluate quantitatively the deceleration and heating effects of pickup protons, the overall compression of the magnetic field in the outer heliosphere caused by deceleration, and the weakening of corotating interaction regions by the thermal pressure of pickup protons.
Context. Up to now, three succesive full-sky maps of heliospheric fluxes of KeV-energetic neutral H-atoms have been registered with the satellite IBEX. The most outstanding feature persisting in these maps is the so-called ribbon which appears as an arc around the upwind direction with unexpectedly high fluxes. This radiation feature was not predicted by models, but at present is tentatively explained as due to energetic plasma sites outside the heliosphere in regions beyond the heliopause. Aims: Since all these proposed explanations, however, need to rely on unproven energizing ion processes, we shall investigate in this article alternative ion sources of keV-ENAs that in contrast appear much closer to the sun, but are based on a clear concept of ion energization to KeV energies, namely suprathermal pick-up ions at a few AU inside and outside of the solar wind termination shock. Methods: Using well-established models for the solar wind magnetic field and the heliospheric TS surface, we derive skymaps of the magnetic field tilt angle, the resulting injection efficiency and the resulting ENA flows. The results are normalised to the ion flux observations made by Voyager-1. We also discuss basic modifications of the TS geometry within the framework of the model. Results: We calculate ENA fluxes of these pick-up ions and show that they, due to their sensitivities to magnetic tilt angles at the termination shock surface, reveal a radiative sickle feature around the upwind direction which in many of its properties resembles the ENA ribbon feature seen by IBEX, although the highest IBEX intensities do not seem to be quantitatively representable by our calculations.
The 3D structure of solar wind and its evolution in time is needed for
heliospheric modeling and interpretation of energetic neutral atoms
observations. We present a model to retrieve the solar wind structure in
heliolatitude and time using all available and complementary data sources. We
determine the heliolatitude structure of solar wind speed on a yearly time grid
over the past 1.5 solar cycles based on remote-sensing observations of
interplanetary scintillations, in situ out-of-ecliptic measurements from
Ulysses, and in situ in-ecliptic measurements from the OMNI-2 database. Since
the in situ information on the solar wind density structure out of ecliptic is
not available apart from the Ulysses data, we derive correlation formulae
between solar wind speed and density and use the information on the solar wind
speed from interplanetary scintillation observations to retrieve the 3D
structure of solar wind density. With the variations of solar wind density and
speed in time and heliolatitude available we calculate variations in solar wind
flux, dynamic pressure and charge exchange rate in the approximation of
stationary H atoms.
The goal of the Fully Online Datacenter of Ultraviolet Emissions (FONDUE)
Working Team of the International Space Science Institute in Bern, Switzerland,
was to establish a common calibration of various UV and EUV heliospheric
observations, both spectroscopic and photometric. Realization of this goal
required an up-to-date model of spatial distribution of neutral interstellar
hydrogen in the heliosphere, and to that end, a credible model of the radiation
pressure and ionization processes was needed. This chapter describes the solar
factors shaping the distribution of neutral interstellar H in the heliosphere.
Presented are the solar Lyman-alpha flux and the solar Lyman-alpha resonant
radiation pressure force acting on neutral H atoms in the heliosphere, solar
EUV radiation and the photoionization of heliospheric hydrogen, and their
evolution in time and the still hypothetical variation with heliolatitude.
Further, solar wind and its evolution with solar activity is presented in the
context of the charge exchange ionization of heliospheric hydrogen, and in the
context of dynamic pressure variations. Also the electron ionization and its
variation with time, heliolatitude, and solar distance is presented. After a
review of all of those topics, we present an interim model of solar wind and
the other solar factors based on up-to-date in situ and remote sensing
observations of solar wind. Results of this effort will further be utilised to
improve on the model of solar wind evolution, which will be an invaluable asset
in all heliospheric measurements, including, among others, the observations of
Energetic Neutral Atoms by the Interstellar Boundary Explorer (IBEX).
