159 research outputs found
Solar cycle influence on the interaction of the solar wind with Local Interstellar Cloud
We present results of a new time-dependent kinetic model of the H atom penetration through the solar wind - interstellar medium interaction region. A kinetic 6D (time, two dimensions in space, and three dimensions in velocity-space) equation for interstellar H atoms was solved self-consistently with time-dependent Euler equations for the solar wind and interstellar charged components. We study the response of the interaction region to 11-year solar cycle variations of the solar wind dynamic pressure. It is shown that the termination shock location varies within ±7 AU, the heliopause variation is ~4 AU, and the bow shock variation is negligible. At large heliocentric distances, the solar cycle induces 10-12% fluctuations in the number density of both primary and secondary interstellar H atoms and atoms created in the inner heliosheath. We underline the kinetic behavior of the fluctuations of the H atom populations. Closer to the Sun the fluctuations increase up to 30-35% at 5 AU due to solar cycle variation of the charge exchange rate. Solar cycle variations of interstellar H atoms in the heliospheric interface and within the heliosphere may have major importance for the interpretation of H atom observations inside the heliosphere
Effect of the heliospheric interface on the distribution of interstellar hydrogen atom inside the heliosphere
This paper deals with the modeling of the interstellar hydrogen atoms (H
atoms) distribution in the heliosphere. We study influence of the heliospheric
interface, that is the region of the interaction between solar wind and local
interstellar medium, on the distribution of the hydrogen atoms in vicinity of
the Sun. The distribution of H atoms obtained in the frame of the
self-consistent kinetic-gasdynamic model of the heliospheric interface is
compared with a simplified model which assumes Maxwellian distribution of H
atoms at the termination shock and is called often as 'hot' model. This
comparison shows that the distribution of H atoms is significantly affected by
the heliospheric interface not only at large heliocentric distances, but also
in vicinity of the Sun at 1-5 AU. Hence, for analysis of experimental data
connected with direct or undirect measurements of the interstellar atoms one
necessarily needs to take into account effects of the heliospheric interface.
In this paper we propose a new model that is relatively simple but takes into
account all major effects of the heliospheric interface. This model can be
applied for analysis of backscattered Ly-alpha radiation data obtained on board
of different spacecraft.Comment: published in Astronomy Letter
Model of the tail region of the heliospheric interface
Physical processes in the tail of the solar wind interaction region with the
partially ionized local interstellar medium are investigated in a framework of
the self-consistent kinetic-gas dynamic model. It is shown that the charge
exchange process of the hydrogen atoms with the plasma protons results in
suppression of the gas dynamic instabilities and disappearance the contact
discontinuity at sufficiently (~3000 AU) large distances from the Sun. The
solar wind plasma temperature decreases and, ultimately, the parameters of the
plasma and hydrogen atoms approach to the corresponding parameters of the
unperturbed interstellar medium at large heliocentric distances.Comment: first version, final version is published in Astronomy Letters vol.29
N.1, pp.58-63, 200
Solar ions in the heliosheath: a possible new source of heavy neutral atoms
We show that multiply ionized coronal C, N, O, Mg, Si, S ions carried by the
solar wind and neutralized by consecutive electron captures from neutral
interstellar atoms constitute an important new source of neutral atoms in the
inner heliosheath, with energies up to ~ 1 keV/n. In the model we developed,
the heavy ions are treated as test particles carried by hydrodynamic plasma
flow (with a Monte-Carlo description of interstellar neutrals) and undergoing
all relevant atomic processes determining the evolution of all charge-states of
considered species (radiative and dielectronic recombination, charge exchange,
photo-, and electron impact ionization). The total strength of the source is
from ~10^6 g/s for S to ~10^8 g/s for O, deposited as neutrals below the
heliopause. These atoms should provide, as they drift to supersonic wind
region, important sources of PUIs and eventually ACRs, especially for species
that are excluded from entering the heliosphere because of their ionization in
the LISM. The expected corresponding ENA fluxes at 1 AU are in the range 10^-4
- 10^0 at./(cm^2 s sr), depending on the species and direction (Table 2).Comment: Submitted for IGGP Astrophysics Conference, March 2006; 6 page
The strong effect of electron thermal conduction on the global structure of the heliosphere
Voyager 1 and 2 crossed the heliopause at 122 AU in 2012 and 119
AU in 2018, respectively. It was quite a surprise because the thickness of the
inner heliosheath obtained by the existing at that time models of the global
heliosphere was significantly larger (by 20-40 AU). Until now, the problem of
the heliosheath thickness has not been fully resolved. Earlier in the frame of
an oversimplified toy model of nearly isothermal solar wind plasma it has been
shown that the effect of electron thermal conduction may significantly reduce
the thickness of the inner heliosheath.
In this paper, we present the first results of our 3D kinetic-MHD model of
the global heliosphere, where the effect of thermal electron conduction has
been considered rigorously. The thermal conduction acts mainly along the
magnetic field lines. Classical and saturated thermal fluxes are employed when
appropriate.
It is shown the effects of thermal conduction are significant. The thickness
of the inner heliospheric is reduced. It is desired effect since it helps to
reconcile the thickness obtained in the model with Voyager data. The other
effects are the strong depletion of the heliosheath plasma temperature toward
the heliopause and the increase of the plasma temperature in the supersonic
solar wind upstream of the termination shock.Comment: 7 pages, 5 figures, accepted for publication in MNRA
Shock-wave heating mechanism of the distant solar wind: explanation of Voyager-2 data
One of the important discoveries made by Voyager-2 is the nonadiabatic radial
profile of the solar wind proton temperature. This phenomenon has been studied
for several decades. The dissipation of turbulence energy has been proposed as
the main physical process responsible for the temperature profile. The
turbulence is both convected with the solar wind and originated in the solar
wind by the compressions and shears in the flows and by pick-up ions. The
compression source of the solar wind heating in the outer heliosphere appears
due to shock waves, which originated either in the solar corona or in the solar
wind itself. The goal of this work is to demonstrate that the shock-wave
heating itself is enough to explain the temperature profile obtained by
Voyager-2. The effect of shock-wave heating is demonstrated in the frame of a
very simple spherically symmetric high-resolution (in both space and time)
gas-dynamical data-driven solar wind model. This data-driven model employs the
solar-wind parameters at 1 AU with minute resolution. The data are taken from
the NASA OMNIWeb database. It is important to underline that (1) the model
captures the shocks traveling and/or originating in the solar wind, and (2)
other sources of heating are not taken into account in the model. We extended
this simple model to the magnetohydrodynamic (MHD) and two-component models and
found very similar results. The results of the numerical modeling with the
one-minute OMNI data as the boundary condition show very good agreement with
the solar-wind temperature profiles obtained by Voyager-2. It is also
noteworthy that the numerical results with daily averaged OMNI data show a very
similar temperature profile, while the numerical runs with 27-day-averaged OMNI
data demonstrate the adiabatic behavior of the temperature.Comment: 12 pages, 7 figure
Two-component model of the interaction of an interstellar cloud with surrounding hot plasma
We present a two-component gasdynamic model of an interstellar cloud embedded
in a hot plasma. It is assumed that the cloud consists of atomic hydrogen gas,
interstellar plasma is quasineutral. Hydrogen atoms and plasma protons interact
through a charge exchange process. Magnetic felds and radiative processes are
ignored in the model. The influence of heat conduction within plasma on the
interaction between a cloud and plasma is studied. We consider the extreme case
and assume that hot plasma electrons instantly heat the plasma in the
interaction region and that plasma flow can be described as isothermal. Using
the two-component model of the interaction of cold neutral cloud and hot
plasma, we estimate the lifetime of interstellar clouds. We focus on the clouds
typical for the cluster of local interstellar clouds embedded in the hot Local
Bubble and give an estimate of the lifetime of the Local interstellar cloud
where the Sun currently travels. The charge transfer between highly charged
plasma ions and neutral atoms generates X-ray emission. We assume typical
abundance of heavy ions for the Local Bubble plasma and estimate the X-ray
emissivity due to charge exchange from the interface between cold neutral cloud
and hot plasma. Our results show that charge exchange X-ray emission from the
neutral-plasma interfaces can be a non-negligible fraction of the observed
X-ray emission.Comment: 9 pages, 7 figure
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