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| Titel |
A comparison study between observations and simulation results of Barghouthi model for O+ and H+ outflows in the polar wind |
| VerfasserIn |
I. A. Barghouthi, S. H. Ghithan, H. Nilsson |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 29, no. 11 ; Nr. 29, no. 11 (2011-11-22), S.2061-2079 |
| Datensatznummer |
250017127
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| Publikation (Nr.) |
 copernicus.org/angeo-29-2061-2011.pdf |
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| Zusammenfassung |
| To advance our understanding of the effect of wave-particle interactions on
ion outflows in the polar wind region and the resulting ion heating and
escape from low altitudes to higher altitudes, we carried out a comparison
between polar wind simulations obtained using Barghouthi model with
corresponding observations obtained from different satellites. The
Barghouthi model describes O+ and H+ outflows in the polar wind
region in the range 1.7 RE to 13.7 RE, including the effects of
gravity, polarization electrostatic field, diverging geomagnetic field
lines, and wave-particle interactions. Wave-particle interactions were
included into the model by using a particle diffusion equation, which
depends on diffusion coefficients determined from estimates of the typical
electric field spectral density at relevant altitudes and frequencies. We
provide a formula for the velocity diffusion coefficient that depends on
altitude and velocity, in which the velocity part depends on the
perpendicular wavelength of the electromagnetic turbulence λ⊥.
Because of the shortage of information about λ⊥, it was
included into the model as a parameter. We produce different simulations
(i.e. ion velocity distributions, ions density, ion drift velocity, ion
parallel and perpendicular temperatures) for O+ and H+ ions, and
for different λ⊥. We discuss the simulations in terms of
wave-particle interactions, perpendicular adiabatic cooling, parallel
adiabatic cooling, mirror force, and ion potential energy. The main findings
of the simulations are as follows: (1) O+ ions are highly energized at
all altitudes in the simulation tube due to wave-particle interactions that
heat the ions in the perpendicular direction, and part of this gained energy
transfer to the parallel direction by mirror force, resulting in
accelerating O+ ions along geomagnetic field lines from lower altitudes
to higher altitudes. (2) The effect of wave-particle interactions is
negligible for H+ ions at altitudes below ~7 RE, while it is
important for altitudes above 7 RE. For O+ wave particle
interaction is very significant at all altitudes. (3) For certain λ⊥ and at points, altitudes, where the ion gyroradius is equal to or
less than λ⊥, the effect of wave-particle interactions is
independent of the velocity and it depends only on the altitude part of the
velocity diffusion coefficient; however, the effect of wave-particle
interactions reduce above that point, called saturation point, and the
heating process turns to be self-limiting heating. (4) The most interesting
result is the appearance of O+ conics and toroids at low altitudes and
continue to appear at high altitudes; however, they appear at very high
altitudes for H+ ions. We compare quantitatively and qualitatively
between the simulation results and the corresponding observations. As a
result of many comparisons, we find that the best agreement occurs when
λ⊥ equals to 8 km. The quantitative comparisons show that many
characteristics of the observations are very close to the simulation
results, and the qualitative comparisons between the simulation results for
ion outflows and the observations produce very similar behaviors. To our
knowledge, most of the comparisons between observations (ion velocity
distribution, density, drift velocity, parallel and perpendicular
temperatures, anisotropy, etc.) and simulations obtained from different
models produce few agreements and fail to explain many observations (see Yau
et al., 2007; Lemaire et al., 2007; Tam et al., 2007; Su et al., 1998;
Engwall et al., 2009). This paper presents many close agreements between
observations and simulations obtained by Barghouthi model, for O+ and
H+ ions at different altitudes i.e. from 1.7 RE to 13.7 RE. |
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