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| Titel |
O+ and H+ ion heat fluxes at high altitudes and high latitudes |
| VerfasserIn |
I. A. Barghouthi, H. Nilsson, S. H. Ghithan |
| 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 ; 32, no. 8 ; Nr. 32, no. 8 (2014-08-26), S.1043-1057 |
| Datensatznummer |
250121101
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| Publikation (Nr.) |
 copernicus.org/angeo-32-1043-2014.pdf |
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| Zusammenfassung |
| Higher order moments, e.g., perpendicular and parallel heat fluxes, are
related to non-Maxwellian plasma distributions. Such distributions are common
when the plasma environment is not collision dominated. In the polar wind and
auroral regions, the ion outflow is collisionless at altitudes above about
1.2 RE geocentric. In these regions wave–particle interaction is
the primary acceleration mechanism of outflowing ionospheric origin ions. We
present the altitude profiles of actual and "thermalized" heat fluxes for
major ion species in the collisionless region by using the Barghouthi model. By
comparing the actual and "thermalized" heat fluxes, we can see whether the heat
flux corresponds to a small perturbation of an approximately bi-Maxwellian
distribution (actual heat flux is small compared to "thermalized" heat
flux), or whether it represents a significant deviation (actual heat flux equal or
larger than "thermalized" heat flux). The model takes into account ion
heating due to wave–particle interactions as well as the effects of
gravity, ambipolar electric field, and divergence of geomagnetic field lines.
In the discussion of the ion heat fluxes, we find that (1) the role of the
ions located in the energetic tail of the ion velocity distribution function
is very significant and has to be taken into consideration when modeling the
ion heat flux at high altitudes and high latitudes; (2) at times the parallel
and perpendicular heat fluxes have different signs at the same altitude. This
indicates that the parallel and perpendicular parts of the ion energy are
being transported in opposite directions. This behavior is the result of many
competing processes; (3) we identify altitude regions where the actual heat
flux is small as compared to the "thermalized" heat flux. In such regions
we expect transport equation solutions based on perturbations of
bi-Maxwellian distributions to be applicable. This is true for large altitude
intervals for protons, but only the lowest altitudes for oxygen. |
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