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| Titel |
A Monte Carlo simulation of the effect of ion self-collisions on the ion velocity distribution function in the high-latitude F-region |
| VerfasserIn |
I. A. Barghouthi, A. R. Barakat, R. W. Schunk |
| 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 ; 12, no. 10/11 ; Nr. 12, no. 10/11, S.1076-1084 |
| Datensatznummer |
250010346
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| Publikation (Nr.) |
 copernicus.org/angeo-12-1076-1994.pdf |
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| Zusammenfassung |
| Non-Maxwellian ion velocity distribution
functions have been theoretically predicted and confirmed by observations, to
occur at high latitudes. These distributions deviate from Maxwellian due to the
combined effect of the E×B drift and
ion-neutral collisions. The majority of previous literature, in which the effect
of ion self-collisions was neglected, established a clear picture for the ion
distribution under a wide range of conditions. At high altitudes and/or for
solar maximum conditions, the ion-to-neutral density ratio increases and, hence,
the role of ion self-collisions becomes appreciable. A Monte Carlo simulation
was used to investigate the behaviour of O+ ions that are E×B-drifting
through a background of neutral O, with the effect of O+ (Coulomb)
self-collisions included. Wide ranges of the ion-to-neutral density ratio ni/nn
and the electrostatic field E were considered in order to investigate the
change of ion behaviour with solar cycle and with altitude. For low altitudes
and/or solar minimum (ni/nn≤ 10-5),
the effect of self-collisions is negligible. For higher values of ni/nn,
the effect of self-collisions becomes significant and, hence, the non-Maxwellian
features of the O+ distribution are reduced. For example, the
parallel temperature Ti\Vert increases, the
perpendicular temperature Ti⊥ decreases, the
temperature anisotropy approaches unity and the toroidal features of the ion
distribution function become less pronounced. Also, as E increases, the
ion-neutral collision rate increases, while the ion-ion collision rate
decreases. Therefore, the effect of ion self-collisions is reduced. Finally, the
Monte Carlo results were compared to those that used simplified collision models
in order to assess their validity. In general, the simple collision models tend
to be more accurate for low E and for high ni/nn. |
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